Allah, the Wise, has said:
اِنَّ اللهَ ياَمُرُكُمْ اَنْ تُؤَدُّوا الْاَماَناَتِ اَليَ اَهْلِهَا
"Surely Allah commands you to render back your trusts to their owners" 
Imam Baqir (a.s.) said:
فَلَوْ اَنَّ قاَتِلَ عَلِيّ بْنِ اَبيِ طاَلِب انْتَمَنَى عَلىَ اَماَنَةٍ لَاَدَّيْتُهاَ اِلَيْهِ
"If the murderer of Imam A'li (a.s.) places a trust in my possession, I would surely return it back to him" 
If anything is placed in trust with someone, safeguarding of that thing is obligatory and unfaithfulness with respect to it is prohibited, irrespective of whether its owner is a believer or a disbeliever.
A trustworthy person, as a result of safeguarding people’s belongings, becomes the beneficiary of God’s grace and favour.
A person who is unfaithful towards people’s trust can be compared to a thief and God cloaks such a person with poverty and indigence.
One of the signs of perfect faith is not being unfaithful towards the trusts.
A trust can be in the form of money, things or even secrets. Shaitan leads astray a trustworthy person by causing him to become unfaithful towards the trust placed with him.
1 - Trustworthiness of Umme Salamah
When Imam A'li (a.s.) decided to move to Iraq and settle there, he handed his letters and testament to Umme Salamah, who in turn passed them over to Imam Hasan (a.s.) on his return to Madinah.
In a similar manner, when Imam Husain (a.s.) set out for Iraq, he too placed his letters and testament in the custody of Umme Salamah with instructions that she should hand them over to his eldest son whenever he sought them from her. After the martyrdom of Imam Husain (a.s.), Imam Sajjad (a.s.) returned to Madinah and she handed documents over to him.
U'mar, the son of Umme Salamah, narrates:
"My mother said: Once, the Holy Prophet (s.a.w.), accompanied by A'li (a.s.), came to my house and asked for a sheepskin. After I had handed it to him, he wrote something on the sheepskin and returned it to me with the instruction: "Whoever seeks this trust from you after mentioning these signs, hand it over to him."
As time passed, the Holy Prophet (s.a.w.) departed from this world. Time passed and Imam Ali (a.s.) became Caliph and still nobody came to claim this trust.
"On the day when the people pledged allegiance to A'li (a.s.), I was seated among them. As he stepped down from the pulpit, the Imam’s eyes fell on me whereupon he said: Seek permission from your mother for I wish to meet her.
I hurried to my mother and as soon as I informed her of Imam’s (a.s.) request, she announced that she had been waiting for that day."
The Imam (a.s.) entered and asked Umme Salamah to hand him the trust which contained certain signs.My mother got up and took out a small chest from inside a larger one and handed it to him. Then, she turned to me and advised: "Do not forsake A'li (a.s.), for none other than him is the rightful Imam after the Holy Prophet (s.a.w.)." 
2 –The Unfaithful Grocer
During the rule of A’zud al-Daulah Dailami, a stranger once came to Baghdad wishing to sell a necklace worth a thousand dinars, but could not find any purchaser for it. As he intended to travel to Makkah, he began to search for a trustworthy person who would safeguard his necklace.
The people pointed him to a grocer who was known for his piety. The stranger placed the necklace in the grocer’s trust and proceeded towards Makkah.
When he returned from Makkah, he approached the grocer and presented him with some gifts that he had brought with him. To the stranger’s great surprise, the grocer pretended as if he did not know him and denied having possession of anything belonging to him. A quarrel ensued, as a result of which, people gathered and threw the person out of the ‘pious’ grocer’s shop.
The person approached the grocer for his necklace several times, only to receive abuse and invectives.
Someone advised him to complain to King A’zud al-Daulah Dailami.Heeding the advice, the man wrote a letter to the king, who replied:
"For three days, wait by the door of the grocery. On the fourth day, I shall pass there and when I greet you, reply to my greetings. The following day, seek your necklace from thegrocer and then inform me of the outcome."
The person did as instructed. On the fourth day, the king, with great pomp and grandeur, passed by the grocery and as soon as his eyes fell upon the person from Baghdad, he greeted him. The person returned the greeting. The king, exhibiting great respect and esteem, began to complain:
"You have come from Baghdad but you did not deem it fit to honour me with a visit and to grant me an opportunity to provide you with accommodation and comfort."
The stranger apologized for not having informed the king of his arrival.
All the while, the grocer and the people around him, looked on in amazement, wondering who this person was who was revered so greatly by the king. The grocer began to fear for his life.
As soon as the king’s procession had passed, the grocer turned towards the stranger and said:
"Brother, when exactly did you place that necklace with me? Did it have any marks? Let me have another look, perhaps I might just be able to locate it." The person described his necklace and the grocer, after a short search, found it.
He handed it over to the person and said:"God is aware of the fact that it had simply slipped out of my mind."
Arriving before the king, the person related the entire episode to him. The king ordered the grocer to be arrested, placed the necklace around his neck and sent him to the gallows. He then ordered the following announcement to be made all over the city:
"Such is the punishment for anyone who takes possession of a trust and then denies it. O’ People! Do take heed from this incident!"
The king then returned the necklace to the stranger from Baghdad and sent him to his own city.
3 – Remaining Faithful when Someone Trusts you
A'bdullah Ibn Sinaan says:
"I approached Imam Sadiq (a.s.) in the mosque at a time when he had completed his A’sr prayers and was sitting down facing the Qiblah. I asked him:
"Some of the governors and rulers consider us to be trustworthy and thus place their wealth with us, but at the same time, they do not pay their ‘khums’. Do we return their money to them or do we keep it for our use?"
The Imam (a.s.) replied three times,"By the Lord of the Ka’bah! Even if Ibn Muljam, the murderer of my father A'li (a.s.), were to place something in trust with me, I would return it to him whenever he wanted it back."
4 - The Shepherd and the Jews’ Sheep
In the year 7 A.H., the Holy Prophet (s.a.w.) with an army of one thousand and six hundred soldiers, set out to conquer the fort of Khaibar, which was about 96 miles from Madinah. The Muslim soldiers had stationed themselves in the desert around Khaibar for sometime but the conquest of the fort remained elusive. During this period, they found themselves in a very difficult situation as far as food was concerned. The lack of food and intense hunger forced them to eat animals like horses and mules, whose meat is disapproved by Islam.
In these circumstances, a black shepherd, who used to graze the sheep of the Jews, arrived in the presence of the Holy Prophet (s.a.w.). He embraced Islam and then said to the Holy Prophet:
"These sheep belong to the Jews and I hereby hand them over to you."
The Holy Prophet (s.a.w.) replied unequivocally:
"These goats have been placed in your possession as a trust and in our religion it is forbidden to be unfaithful to one’s trust. It is incumbent upon you to lead the sheep to the door of the fort and hand them over to their owners."
The shepherd, in compliance with his orders, handed the sheep over to their respective owners and then returned to join the Muslim army.
5 – Possessions Entrusted to the Holy Prophet (s.a.w.)
When the Holy Prophet (s.a.w.) migrated from Makkah to Madinah, he left behind Amirul Mu'mineen in Makkah so that he could return the possessions entrusted to the Prophet, back to their respective owners.
Handhalah Ibn Abi Sufiyaan instructed U’mair Ibn Waail to go to A'li and tell him:
"I had placed one hundred mithqaal  of gold with the Holy Prophet (s.a.w.). Since he has fled to Madinah and you are his representative here, please handmy property back to me." Handhalah added that if A’li asked for witnesses to support the claim, all the Quraish would testify to the veracity of U’mair’s claim.
Initially, U’mair was hesitant but Handhalah enticed him by presenting him with some gold and a necklace belonging to Hind, the wife of Abu Sufiyaan.
U’mair approached A'li (a.s.) and made the claim, adding thatAbu Jahl, I’krimah, U’qbah, Abu Sufiyaan and Handhalah would testify for him.
The Imam (a.s.) retorted, "May their deception rebound on themselves", and then asked him to bring his witnesses near the Ka’bah. When all of them had arrived, he began questioning each one, individually and separately, about the items being held in trust.
"What time was it when you had placed your possession with Muhammad (s.a.w.)?" he questioned U’mair first.
"It was morning when I gave him the gold and he handed it over to his servant," replied U’mair.
H. Ali (a.s.) asked Abu Jahl the same question.
He replied, "I have no idea."
When Abu Sufiyaan was questioned, he responded, "It was at sunset and he had placed it in his sleeves."
When Handhalah was questioned, he gave the answer,"He took possession of the gold at the time of Dhuhr and placed it in front of him."
When U’qbah was questioned, he replied, "It was A’sr when the Prophet took the possession in his own hands and carried it to his house."
And finally, when the Imam (a.s.) questioned I’krimah, he answered, "It was bright and early in the morning when Muhammad (s.a.w.) took possession of it and sent it to the house of Fatimah (a.s.)."
The Imam (a.s.) then informed them of their conflicting statements and their deception thus became apparent.
Then, turning to U’mair, he asked him, "Why was it that while you lied, you appeared uneasy and your face had gone pale?"
U’mair replied, "By the Lord of the Ka’bah! I had not placed anything in trust with Muhammad (s.a.w.). It was a deception Handhalah had bribed me into. This necklace here, belonging to Hind, with her name inscribed on it, is one of the things presented to me as a bribe."
 Holy Qur'an, ch. Al-Nisaa (4), vs. 58.
 Al-Kafi, vol. 5, pg. 133
 Safinah al-Bihaar, under ‘سلم’
 Payghambar Wa Yaaraan, vol. 1, pg. 275; Bihaar al-Anwaar vol. 6, pg. 942.
 Pand-e-Taareekh, vol. 1, pg. 202; Mustatraf, vol. 1, pg. 118.
 Namunah-e-Ma'arif, vol. 1, pg. 354; Bihaar al-Anwaar vol. 15, pg. 149.
 Daastaan-ha Wa Pand-ha, vol. 8, pg. 114; Seerah Ibn Hishaam, vol. 3, pg. 344.
 A weight, equivalent to 5 grams.
 Rahnamaa-e-Sa’adat, vol. 2, pg. 435; Naasikh al-Tawaareekh - Amirul Mu'mineen, pg. 676.