Allah, the Wise, has said:
فَإِِذاَ عَزَمْتَ فَتَوَکَّلْ عَلى اللٌّهِ اِنَّ اللٌّهَ يُحِـبُّ الْمُتَوَکِّلِيْنَ
"So when you have decided, then place your trust in Allah; surely Allah loves those who trust." 
Imam Ali (as) said:
أَلتَّوَكُّلُ عَلى اللٌّهِ نَجاَةٌ مِنْ كُلِّ سُوْءٍ.
"Placing one's trust in Allah is the means of deliverance from every evil." 
Tawakkul (placing one's trust in Allah) is a jar that has been sealed with Allah's seal, and only that person who does not rely on Allah and place his trust in Him, shall break open the seal of the jar and consume its contents.
The lowest grade of tawakkul is when a person does not strive to act upon his own principles before the right time, and does not endeavour to acquire more than what has been ordained for him. The essence of tawakkul is entrusting one's affairs to Allah, and if a person is heedless towards the actual 'cause', i.e. Allah, he shall not achieve the reality of tawakkul.
Tawakkul can never be realized by mere words and claims, rather, it is an internal and esoteric issue, which finds its roots in faith and belief, and it is by abandoning all hopes and aspirations that a person can arrive at the reality of tawakkul.
1 – The Trader who Placed his Trust in Allah
During the time of the Noble Prophet (sa) there lived a trader who, in all affairs, always placed his trust in Allah. He used to travel from Syria to Madinah for trade and during one of his trips, he was confronted by a bandit who drew his sword and intended to kill him.
"If it is my wealth that you desire, come and take it and leave me alone," pleaded the trader.
"Killing you is a must, for if I let you go free, you will identify me to the authorities," said the bandit.
"In that case give me respite till I have offered a two rak'at prayer," requested the trader.
The bandit agreed and the trader engaged himself in prayers. Having completed the prayers, he raised his hands and beseeched: 'O' Lord! I have heard from Your Prophet that whoever places his trust in You shall remain protected. I have no helper in this desert and Your grace is my only hope.'
Having placed all his trust in Allah, he had hardly completed his supplication when a rider on a white horse loomed in the distance. When he came close, the rider confronted the bandit and killed him with one stroke of his sword. Then, turning to the trader, he said: "O' You, who places your trust in Allah! I have killed the enemy of Allah and He has delivered you from him."
"Who are you that you have come to my assistance in this desert?" the trader asked.
"I am your tawakkul. Allah brought me out in the form of an Angel and I was in the heavens when Jibra`il called out to me and said: "Hasten to the assistance of your master and exterminate his enemy", and here I have come and eliminated your enemy." Having said thus, he disappeared out of sight.
The trader fell down in prostration of thanksgiving to Allah and acquired a stronger conviction with respect to the instructions of the Noble Prophet (sa) regarding tawakkul. On arrival in Madinah, he approached the Noble Prophet (sa) and narrated what had transpired.
"Indeed! Tawakkul raises a person to the pinnacle of success and the rank of a person who possesses it, is equivalent to the ranks of the Prophets, the friends of Allah, the righteous ones and the martyrs," said the Prophet (sa).)
2 - The Noble Prophet and Trust in Allah
When Abu Sufiyan, the chief of the polytheists of Makkah, saw the ten thousand strong army of Islam (during the conquest of Makkah), he was filled with awe and astonishment. As he walked beside the battalions of the Noble Prophet (sa), he murmured: "I wish I knew why Muhammad became victorious over me. How did he manage to gather for himself such a powerful army despite being alone and without support in Makkah?"
The Noble Prophet (sa) overheard him. "We became victorious over you by Allah's assistance!" he said, placing his hand upon Abu Sufiyan's shoulder.
In the battle of Hunain, when the enemy suddenly and unsuspectingly attacked the forces of Islam, chaos reigned supreme within the Muslim ranks. When the Noble Prophet (sa) watched this state of the Muslim army, he sought Allah's help by placing his trust in Him, and supplicated: 'O' Lord! All praise and thanks only belong to You. I place my complaint (regarding the state of affairs) before You and it is only You from whom help and assistance ought to be sought.'
At that moment, Jibra`il descended from the heavens and said to him: "O' Prophet of Allah! You have recited a supplication which Musa (as) had recited when the sea had split for him and he was granted deliverance from the evils of Firaawn."
3 - The Illness of Prophet Musa
Once, Prophet Musa (as) became ill. The Bani Israel came to him and realizing what his illness was, advised him: "If you consume such and such medicine you will recover from your sickness."
"I shall not seek any cure but will instead wait till Allah cures me without the help of any medicine," said Musa (as) to them. His illness became prolonged whereupon Allah revealed to him: "By My Majesty and Glory! I shall never cure you till you have consumed the medicine which they had recommended to you."
Musa (as) asked the Bani Israel to treat him with the medicine that they had previously suggested. They treated him and shortly after that, Musa (as) regained his health. However, this incident left Musa (as) with a feeling of complaint and dejection but Allah revealed to him: "You desired to annul My Wisdom by means of your trust in Me! Is there one, other than Me, who has placed the medicinal and beneficial effects in plants and various things?" 
4 - Hammad Ibn Habib
Hammad Ibn Habib Kufi narrates: "One year, I had set out for Hajj accompanied by some people. Just as we passed by a place called Zubalah, a dreadful wind with black dust began to blow. Its intensity was so great and severe that everyone in the group were left scattered. I found myself alone and lost in a place with no water or trees. It was not long before night fell. Staring into the distance, my eyes perceived the silhouette of a single tree and I began trudging towards it. As I approached the tree, I witnessed that a youth, dressed in white apparel and scented with musk, also came up to the tree.
'This person must be one of the auliya of Allah!' I thought.
I concealed myself fearing that if I came forward, he would move away to another place. The youth readied himself for his prayers, recited:
يَا مَنْ حَاذَ کُلََّ شَيْءٍٍٍ مَلَکُوْتاً
and then started his prayers.
I noticed that there was a spring of water nearby. I performed my ablution and stood behind the youth for my prayers. I observed that in the course of his prayers, when the youth reached the verses that narrated Divine chastisement and punishment, he would repeat them with wailing, weeping and lamentation. After the prayers, the youth began to walk away from his place, all the while supplicating:
يَا مَنْ قَصَدَهُ الضَّالُّون
Fearing that I might lose him, I rushed toward him and pleaded: "I place you under the oath of He Who has taken away exhaustion from you and instilled within you the ecstasy of this solitude! Have pity upon me for I have lost my way and I (also) desire to be adorned with your traits and attributes."
"If you had truly placed your trust in Allah, you would never have lost your way. Now follow me," replied the youth.
Saying this, he went to one side of the tree and, taking hold of my hand, brought me to a place by means of tayy al-ardh). It became apparent to me that morning had dawned.
"Good news for you, for this place is Makkah," said the youth.
I realized that I could hear the voices of the pilgrims who had come there to perform the Hajj. I turned to the youth and asked: "I place you under the oath of He, upon Whom you have pinned your hopes for the Day of Judgment! Tell me, who are you?"
"Since you have placed me under oath, I shall inform you of my identity. I am Ali Ibn Husain (Zainul aھbidin)," the youth answered.'"
5 – Relying upon the Butler
Jibra`il came to Prophet Yusuf (as) while he was in prison and asked him: "O' Yusuf! Who made you the most beautiful of all men?"
Yusuf replied, "Allah."
Jibra`il questioned again, "Who made you the most beloved of all children in the eyes of your father?"
"My Allah," said Yusuf.
"Who directed the caravan towards the well (into which you were thrown)?"
"My Lord," replied Yusuf.
"Who protected you from the stone which the people of the caravan had hurled into the well?"
"Who delivered you from the well?"
"Who protected you from the deceit of the ladies?"
Jibra`il finally concluded, "Allah says: What made you seek your need from someone other than Me? For this act, you shall stay in prison for seven years (for the offense of placing your trust in the king's barman and asking him to seek your freedom from the king)."
According to another tradition, Allah revealed to him: "O' Yusuf! Who was it who showed you that dream?"
Yusuf replied, "It was You, O' My Lord!"
"Who protected you from the guiles of the wife of the King of Egypt?" asked Allah.
"It was You, O' My Lord!"
Allah declared, "(Then) why did you seek help from someone else and not from Me? Had you placed your trust in Me, I would have liberated you from your imprisonment, but now that you have placed your trust in someone else, you must stay in prison for seven years."
(After this) Yusuf wept so much in prison that his inmates became frustrated with him and it was decided that he would only weep on alternate days. 
 Noble Qur'an, Surat ale Imran (3), Verse 159
 Biharul Anwar, Volume 78, Page 79
 Tadhkerah al-Haqaiq, Page 72
 Khazinatul Jawahir, Page 679; Majalis al-Muttaqin (of Shahid-e-Thalith
 Dars-hai Az Zindagi-e-Payambar-e-Islam, Page 216; Biharul Anwar, Volume 21, Page 150
 Jamea al-Saaadat, Volume 3, Page 228; aIlm-e-Akhlaq-e-Islami, Volume 2, Page 290
 Literally: Folding up of the earth. Covering a great distance in a fraction of a moment, miraculously. (Tr.
 Pand-e-Tarikh, Volume 5, Page 182; Biharul Anwar, Volume 11, Page 24
 Namunah-e-Maaarif, Volume 3, Page 280; Layaliul Akhbar, Page 92