The Quran
“Maintain with care the [obligatory] prayers and [in particular] the middle prayer and stand before Allah, devoutly obedient.” [Qur’an; 2:238]
“But yes, whoever fulfills his commitment and fears Allah – then indeed, Allah loves those who fear Him.” [Quran; 3:76]
“…They will only be reminded who are people of understanding – those who fulfill the covenant of Allah and do not break the contract…” [Qur’an; 13:19-20]
“… And fulfill [every] commitment. Indeed, the commitment is ever [that about which one will be] questioned.” [Qur’an; 17:34]
Hadith
“One who was devoted to the Qur’an will be told to recite, ascend and recite carefully as he recited carefully when he was in the world, for he will reach his abode when he comes to the last verse he recites.” [Abu Dawud]
Yahya related to me from Malik that Yahya ibn Said said, ”Ubada ibn al-Walid ibn Ubada ibn as-Samit informed me from his father that his grandfather (Ubada) said, ‘We made a contract with the Messenger of Allah, may Allah bless him and grant him peace, to hear and obey in ease and hardship, enthusiasm and reluctance, and not to dispute with people in authority and to speak or establish the truth wherever we were without worrying about criticism.’” [Muwatta Malik]
Narrated Abu Huraira: The Prophet (peace and blessings of Allah be upon him) said, “(Allah said), ‘Every good deed of Adam’s son is for him except fasting; it is for Me. and I shall reward (the fasting person) for it.’ Verily, the smell of the mouth of a fasting person is better to Allah than the smell of musk.” [Sahih Bukhari]
“There are four characteristics, whoever has them all is a pure hypocrite, and whoever has one of its characteristics, he has one of the characteristics of hypocrisy, until he gives it up: When he speaks he lies, when he makes a covenant he betrays it, when he makes a promise he breaks it, and when he disputes he resorts to obscene speech.” In the narration of Sufyan (one of the narrators) it is: “And if he has one of them, he has one of the characteristics of hypocrisy.” [Sahih Muslim]
The Prophet (peace and blessings of Allah be upon him) said, ”Every betrayer will have a flag on the Day of Resurrection” [Sahih Bukhari]