The Messenger of Allah said: "Verily actions are by intentions, and for every person is what he intended. So the one whose ‘hijrah’ (migration) was to Allah and His Messenger, then his ‘hijrah’ was to Allah and His Messenger. And the one whose ‘hijrah’ was for the world to gain from it, or a woman to marry her, then his ‘hijrah’ was for what he made ‘hijrah’ for." [Al-Bukhari and Muslim]

Many scholars began books with this Hadeeth. Imam Al-Bukhari commences his book of Hadeeth (Saheeh Al-Bukhari) with this Hadeeth and explains that every action that is done without seeking Allah’s pleasure is invalid and devoid of reward.

It can be said that the entire religion revolves around this Hadeeth. Imam Ash-Shafi'i said, "this Hadeeth constitutes a third of all knowledge."

Muslim scholars differ in opinion as to the limits of the Prophet’s saying: ‘actions are by intentions’. Many of the later scholars are of the opinion that the limit is that the action is made correct or acceptable with the intention. What is meant by this is that a legislated action needs an intention. As for habitual actions such as eating, drinking, dressing, etc., they are not in need of an intention.

Some say 'actions' here is to be understood in its generality; therefore, nothing is exempt from it. Others relate this as the saying of the majority, meaning the majority of the early scholars. This occurs in the words of Ibn Jareer At-Tabari, Abu Talib Al-Makki, and others from the early scholars . Imam Ahmad said: “I like that for every action, from prayer, fasting or charity or any action of righteousness that there be an intention preceding the action. The Prophet said: ‘actions are by intentions’, and this is taken for every matter.”

Fadl Ibn Ziyad said: “I asked Abu Abdullah (Imam Ahmad ) about the intention in action, how should it be? He said: ‘One should concentrate on himself when he intends to do an action, not doing it for the sake of people (showing off).’"

The saying of the Prophet after this: 'and for everyone is what he intended' informs that one cannot gain anything from his action except what he intended. So if he intended good, he gets good. If he intended evil then he gets evil. This second statement (of the Hadeeth) is not merely reiterating the first, because the first statement points to the fact that the goodness or corruptness of the action is according to the intention necessary for that action to exist. The second statement points to the fact that the reward of a person for his action is according to his good intention, and that the punishment for his action is according to his evil intention.

The meaning of ‘intention’ in the speech of the Prophet and the Salaf (righteous predecessors) was used generally to carry the meaning of ‘desire’. In the Quran, the word ‘desire’ is often used to describe an intention, as in Allah’s Saying (which means): "…Among you are some who desire this world, and among you are some who desire the Hereafter…" [Quran 3: 152]

The Messenger said: "People will be gathered upon their intentions." [Ibn Majah] He also said: "Mankind will be resurrected upon their intentions." [Muslim] Another Hadeeth says: "Verily those slain on the battlefield will be resurrected upon their intentions." [Ibn Abi Ad-Dunya]

The Prophet also said: "For the ones whose concern is this world, Allah will scatter his affair, and place poverty between his two eyes. He will not get from the world except what is written for him. For the one whose intention is the Hereafter, Allah will gather for him his affair and place contentment in his heart, and the world will come to him willingly."[Ibn Majah]

Zayd Ash-Shami said: "Verily I like to make an intention for everything I do even if it is eating and drinking."

Sufyan Ath-Thawri said: "I have not treated anything more difficult than my intention, because it keeps changing."

Ibn Al-Mubarak said: "May be a small action is made great by its intention, and may be a great action is made small by its intention."

Imam Ahmad said that the foundation of the religion is upon three Hadeeths:

Fudayl Ibn `Iyadh said about the Saying of Allah (which means): "He who created death and life to test you [as to] which of you is best in deed.” [Quran 67: 2]