Actions are by intentions
On the authority of Omar bin Al-Khattab, who said: I heard the messenger of Allah salla Allah u alihi wa sallam say: “Actions are but by intention and every man shall have but that which he intended. Thus he whose migration was for Allah and His messenger, his migration was for Allah and His messenger, and he whose migration was to achieve some worldly benefit or to take some woman in marriage, his migration was for that for which he migrated.”
Related by Bukhari and Muslim

Islam, Iman, Ihsan
Also on the authority of Omar, who said: One day while we were sitting with the messenger of Allah there appeared before us a man whose clothes were exceedingly white and whose hair was exceedingly black; no signs of journeying were to be seen on him and none of us knew him. He walked up and sat down by the prophet. Resting his knees against his and placing the palms of his hands on his thighs, he said: “O Muhammed, tell me about Islam”. The messenger of Allah said: “Islam is to testify that there is no god but Allah and Muhammed is the messenger of Allah, to perform the prayers, to pay the zakat, to fast in Ramadhan, and to make the pilgrimage to the House if you are able to do so.” He said:”You have spoken rightly”, and we were amazed at him asking him and saying that he had spoken rightly. He said: “Then tell me about eman.”He said:”It is to believe in Allah, His angels, His books, His messengers, and the Last Day, and to believe in divine destiny, both the good and the evil thereof.” He said:”You have spoken rightly”. He said: ” Then tell me about ehsan.” He said: “It is to worship Allah as though you are seeing Him, and while you see Him not yet truly He sees you”. He said: “Then tell me about the Hour”. He said: “The one questioned about it knows no better than the questioner.” He said: “Then tell me about its signs.” He said: “That the slave-girl will give birth to her mistress and that you will see the barefooted, naked, destitute herdsman competing in constructing lofty buildings.” Then he took himself off and I stayed for a time. Then he said: “O Omar, do you know who the questioner was?” I said: “Allah and His messenger know best”. He said: “He was Jebreel (Gabriel), who came to you to teach you your religion.”
Narrated by Muslim

Islam is Built Upon Five
On the authority of Ibn Omar, the son of Omar bin Al-Khattab, may Allah be pleased with both, who said: I heard the messenger of Allah says: “Islam has been built on five [pillars]: testifying that there is no god but Allah and that Muhammed is the messenger of Allah, performing the prayers, paying the zakat, making the pilgrimage to the House, and fasting in Ramadan.”
Related by Bukhari and Muslim

Deeds are by Their Final Actions
On the authority of Abdullah bin Masud, who said: the messenger of Allah, and he is truthful, the believed narrated to us: “Verily the creation of each one of you is brought together in his mother’s belly for forty days in the form of seed, then he is a clot of blood for a like period, then a morsel of flesh for a like period, then there is sent to him the angel who blows the breath of life into him and who is commanded about four matters: to write down his means of livelihood, his life span, his actions, and whether happy or unhappy. By Allah, other than Whom there is no god, verily one of you behaves like the people of Paradise until there is but an arm’s length between him and it, and that which has been written overtakes him and so he behaves like the people of Hell-fire and thus he enters it; and one of you behaves like the people of Hell-fire until there is but an arm’s length between him and it, and that which has been written overtakes him and so he behaves like the people of Paradise and thus he enters it.”
Related by Bukhari and Muslim

Rejection of Evil Deeds and Innovations
On the authority of Aishah, who said: The Messenger of Allah said: “He who innovates something in this matter of ours that is not of it will have it rejected.”
narrated by Bukhari and Muslim

And in one version by Muslim, it reads: “He who does an act which our matter is not [in agreement] with will have it rejected.”

Protecting the Heart
On the authority of Al-Numan bin Basheer, who said: I heard the messenger of Allah says: “That which is lawful is plain and that which is unlawful is plain and between the two of them are doubtful matters about which not many people know. Thus he who avoids doubtful matters clears himself in regard to his religion and his honor, but he who falls into doubtful matters falls into that which is unlawful, like the shepherd who pastures around a sanctuary, all but grazing therein. Truly every king has a sanctuary, and truly Allah’s sanctuary is His prohibitions. Truly in the body, there is a morsel of flesh which, if it is whole, all the body is whole and which, if it be diseased, all of it is diseased. Truly it is the heart.”
Narrated by Bukhari and Muslim

The Religion is Naseehah (Sincere Advice)
On the authority of Tamim Al-Dari that the prophet said: “Religion is sincerity”. We said: “To whom?” He said: “To Allah and His Book, and His messenger, and to the leaders of the Muslims and their common folk”.
Narrated by Muslim

The Sanctity of a Muslim
Abdullah bin Omar narrated that the messenger of Allah said: “I have been ordered to fight against people until they testify that there is no god but Allah and that Muhammed is the messenger of Allah and until they perform the prayers and pay the zakat, and if they do so they will have gained protection from me for their lives and property, unless [they do acts that are punishable] in accordance with Islam, and their reckoning will be with Allah the Almighty.”
Related by Bukhari and Muslim.

Obligations are According to Ability
On the authority of Abu Hurairah, who said: I heard the messenger of Allah says: “What I have forbidden to you, avoid; what I have ordered you [to do], do as much of it as you can. It was only their excessive questioning and their disagreeing with their prophets that destroyed those who were before you.”
Related bu Bukhari and Muslim

Restricting Oneself to the Permissible
On the authority of Abu Hurairah, who said: the messenger of Allah said: “Allah the Almighty is good and accepts only that which is good. Allah has commanded the faithful to do that which he commanded the messengers, and the Almighty has said: “O ye messengers! Eat of the good things and do right”. And Allah the Almighty has said: “O ye who believe! Eat of the good things wherewith We have provided you”
Then he mentioned [the case of] a man who, having journeyed far, is disheveled and dusty and who spreads out his hands to the sky [saying]: “O Lord! O Lord!” – while his food is unlawful, his drink unlawful, his clothing unlawful, and he is nourished unlawfully, so how can he be answered!”
Related by Muslim