Allah, the Wise, has said:
اَوَلَمْ يَتَفَکَّرُوا فِي أََنْفُسِهِمْ مَا خَلَقَ اللٌّهُ السَّمٌواَتِ وَ الأََرْضَ وَ ماَ بَيْنَهُماَ إِلاَّ بِالْحَقِّ وَ أََجَلٍ مُسَمًّى
"Do they not reflect within themselves: Allah did not create the heavens and the earth and what is between them two but with truth, and (for) an appointed term?" 
Imam Ali (as) said:
أَلتَّفَکُّرُ يَدْعُو إِِلـى الْبِرِّ وَ الْعَمَلِ بِهِ.
"Contemplation invites (man) towards good (deed) and its performance." 
Reflecting over one's own state and that of the other people leads to the manifestation of the good, expiation of sins and illumination of the heart. It draws a person's attention towards his Hereafter and brings about an increase in his or her (good) deeds.
Contemplation is a quality and an act of worship, the like of which there is none - just as the Noble Prophet (sa) has said: "An hour of contemplation is superior to an entire year's worship." Only he, upon whose heart Allah has cast His glance and illuminated it with the light of His cognizance, can reach the station of contemplation, whereupon he then begins to perceive the world with a vision of comprehension and understanding, and never becomes heedless of Allah.
1 – Rabiaah
Rabiaah Ibn Kaab reports: "Once, the Noble Prophet (sa) said to me: "O' Rabiaah! You have been serving me for seven years and therefore, will you not ask for something from me in order that I grant it to you?"
"O' Prophet of Allah! Grant me some time in order that I may reflect over the matter," I requested. The next day, when I had arrived in his presence, the Prophet (sa) said: "O' Rabi'ah! Speak out your wish."
"Pray to Allah that He makes me enter Paradise along with you!" I said.
Hearing this request, he inquired, "Who is it that has taught you to seek this from me?"
"No one has taught it to me. I considered that if I sought great wealth, it would eventually get exhausted; if I sought a long life and numerous children, the ultimate eventuality would be death; hence, as a result of this contemplation, I eventually opted for this request," I replied.
The Noble Prophet (sa) lowered his head for a few moments as he deliberated, after which, raising his head, he said: "I shall seek your wish from Allah, but you must help me too (in this matter) by prostrating excessively.")
2 – Contemplation before Action
One of the companions of the Noble Prophet (sa) said to him: "I always tend to suffer losses in my business transactions. The guile and deception of the sellers or the purchasers act like magic and leave me cheated."
The Noble Prophet (sa) advised: "In every transaction in which you fear that you might be deceived, demand from the person with whom you are doing business with the right to annul the transaction within a period of three days. This is for the reason that should you happen to suffer losses, you would be able to take back your money. In addition, be patient and forbearing in the course of the transaction.
"Do know that contemplation and patience are from Allah, while hastiness and impetuosity are from Shaitan. You can learn this lesson from a dog, for when you throw a piece of bread to a dog, it does not immediately begin to eat it but first smells it and after finding it to be appropriate, begins eating it; similarly, you should smell every matter that comes up before you (i.e. reflect and ponder over the pros and cons of it and do not embark upon it without the preliminaries). You, with your intellect and wisdom, are no less than a dog; thus, contemplate and reflect before every action."
3 – Types of Contemplation
Miqdad, one of the loyal companions of Ali (as), says: "I went to Abu Hurairah who said that he had heard the Noble Prophet (sa) say: 'Contemplating for an hour is better than the worship of one year.'
I went to Ibn Abbas and heard him say that the Noble Prophet (sa) said: 'Contemplation for one hour is superior to seven years of worship.'
I went to another companion and heard him narrate that the Noble Prophet (sa) said: 'An hour of contemplation is better than seventy years of worship.'
I was astonished to hear each of them narrating differently from the other and so, I approached the Noble Prophet (sa) and informed him of the three different versions. He said: "All three of them speak the truth." Then, in order to prove his point, he summoned the three men. All of us gathered in the presence of the Noble Prophet (sa).
The Noble Prophet (sa) asked Abu Hurairah: "How do you contemplate?"
"As stated by Allah in the Qur'an: '(Men of understanding) reflect on the creation of the heavens and the earth.'. I too reflect upon the wonders of the heavens and the earth," he replied.
The Noble Prophet (sa) remarked, "One hour of your contemplation is better than one year of worship."
Then turning to Ibn Abbas, he asked, "How do you contemplate?"
"I reflect upon death and the horrors of the Day of Judgment," replied Ibn Abbas.
The Noble Prophet (sa) said, "One hour of your contemplation is better than seven years of worship." Then, he asked the other companion, "In what manner do you contemplate?"
The companion answered, "I reflect upon the fire of Hell and its dreadfulness and severity."
"One hour of your contemplation is better than seventy years of worship," the Noble Prophet (sa) stated.
In this way the issue was solved and it became clear that the rewards for contemplation depended upon the intention that accompanied it.
4 – Thoughts of Leadership
Saadi narrates: "One of my friends who was disturbed and distressed due to his meagre livelihood, complained to me about his low income and a large family."
"In order to safeguard my reputation, I intend to shift to another city so that no one becomes aware of the abject state of my affairs," he said. "You are aware that I know accounting and can maintain accounts; I have approached you so that you use your rank and position to get me a job in the government so that I might lead my remaining life with peace of mind and will be grateful to you for your efforts!"
I said to him, "Handling the accounts of the king entails two aspects; on the one hand it carries hope while on the other hand it is also work which has to be feared. Do not place yourself in an ominous situation for the hope which the work possesses."
"In view of my condition, your advice appears to be inappropriate; in addition, you have not responded correctly to my request," said the friend.
"You surely possess piety, knowledge and trustworthiness but (do realize that) envious and fault-finding individuals lie in wait for you. It is in your own interest that you lead your life with contentment and abandon the idea of a high rank and post," I explained.
My friend was upset when he heard this and said, "What kind of reasoning and deliberation is this? It is in times of need that friends should step forward for help, for in good times even enemies pretend to be one's friend."
Sensing his embarrassment over my advice, I took him to the minister of treasury who was known to me. I narrated to him my friend's plight and the minister assigned him the responsibility of a petty task.
As time passed, the officials found him to be vigilant and pleasant-mannered and so promoted him. After a long time, I embarked on a journey to Makkah with some of my friends. On the way back, not far from my city, I came across my friend who seemed to be in a state of distress. He came towards me looking depressed.
"Why are you in such a state?" I asked him.
"Just as you had predicted, a group of people became envious of me and accused me of treason," he responded. "The king, without any investigation, threw me into prison and subjected me to torture and punishment. I remained in prison till the news of the return of the pilgrims reached the city, whereupon I was set free. The king even went to the extent of confiscating the inheritance which I had received from my father."
Saadi continues: "I said to him, 'I had advised you previously that working for kings is similar to a journey by sea - beneficial, but at the same time, dangerous - you might either strike treasure or end up in destruction, but you refused to take heed!'"
5 – The Kingdom of Rey or Killing the Imam
Yazid instructed his governor, aUbaidullah Ibn Ziyad, that if Husain (as) refused to pledge allegiance, he should fight the Imam (as).
Prior to the incident of Kerbala, aUbaidullah Ibn Ziyad had appointed aUmar Ibn Sa`d as governor of the province of Rey, but before he could go there, aUbaidullah Ibn Ziyad sent him a letter, which contained the following instructions: 'Husain (as) has arrived in Iraq. First proceed to Iraq, fight with him, kill him and then proceed towards Rey.'
aUmar Ibn Saad approached aUbaidullah and requested: "O' Amir! Relieve me of this responsibility!"
"I shall relieve you of this responsibility but I shall also relieve you of the governorship of Rey," aUbaidullah responded.
aUmar Ibn Saad found himself hesitating between fighting the Imam (as) and governing the great kingdom of Rey. He requested aUbaidullah to give him respite for a night so that he could reflect over the matter. aUbaidullah agreed and aUmar Ibn Saad passed the entire night pondering over the matter till he eventually opted for the kingdom of Rey, which lay before him at that moment, but chose to disregard Hell and Paradise, which were in the next life. He decided to fight the Imam (as).
The next morning, he went to aUbaidullah and expressed his readiness to accept the responsibility of fighting the Imam (as). aUbaidullah placed a huge army at his disposal so that he could proceed to Kerbala for the purpose.
Imam Husain (as) entered Kerbala on the 2nd of Muharram while aUmar Ibn Saad, in his capacity as the supreme commander of his army and with a four thousand strong cavalry, arrived there on the 3rd.
He appointed Shimr as the chief of his army and on the 10th of Muharram went to the extent of ordering the killing of Imam Husain (as) and seventy two of his children and companions just for the purpose of acquiring the kingdom of Rey."
 Noble Qur'an, Suratul Rum (30), Verse 8
 Jamea al-Saaadat, Volume 1, Page 166
 Tadhkerah al-Haqaiq, Page 29
 Khazinatul Jawahir, Page 345; Al-Daawat (By Rawandi
 Riwayat-ha Wa Hikayat-ha, Page 195; Dastan-ha-e-Mathnawi, Volume 2, Page 125
 Noble Qur'an, Surat ھle aImran (3), Verse 191
 Dastan-ha Wa Pand-ha, Volume 5, Page 87; Tafsir Ruhul Bayan, Volume 8, Page 440
 Hikayat-ha-e-Gulistan, Page 65
 Muntahal Aamal, Volume 1, Page 333