Imam Al-Nawawi’s Riyad-us-Saliheen
The Righteous conduct on Regular base
Allah, the Exalted, says:
“Has not the time come for the hearts of those who believe (in the Oneness of Allah – Islamic Monotheism) to be affected by Allah’s Reminder (this Qur’an), and that which has been revealed of the truth, lest they become as those who received the Scripture [the Taurat (Torah) and the Injeel (Gospel)] before (i.e., Jews and Christians), and the term was prolonged for them and so their hearts were hardened?” (57:16)
“And We sent `Isa (Jesus) – son of Maryam (Mary), and gave him the Injeel (Gospel). And We ordained in the hearts of those who followed him, compassion and mercy. But the monasticism which they invented for themselves, We did not prescribe for them, but (they sought it) only to please Allah therewith, but that they did not observe it with the right observance.” (57:27)
“And be not like her who undoes the thread which she has spun, after it has become strong…” (16:92)
“And worship your Rubb until there comes unto you the certainty (i.e., death).” (15:99)
And there are Ahadith, one of them is narrated by `Aishah (May Allah be pleased with her): Messenger of Allah (sallallaahu alayhi wa sallam) liked that act of worship most in the performance of which a person was regular and constant.
153. `Umar bin Al-Khattab (May Allah be pleased with him) reported: Messenger of Allah (sallallaahu alayhi wa sallam) said, “Should anyone fall asleep at night and fail to recite his portion of the Qur’an, or a part of it, if he recites it between the Fajr prayer and the Zuhr prayer, it will be recorded for him as though he had recited it during the night”.
154. `Abdullah bin `Amr bin Al-`as (May Allah be pleased with them) reported: Messenger of Allah (sallallaahu alayhi wa sallam) said to me, “O Abdullah! Do not be like so-and-so. He used to get up at night for optional prayer but abandoned it later.”
[Al-Bukhari and Muslim].
155. `Aishah (May Allah be pleased with her) reported: When Messenger of Allah (sallallaahu alayhi wa sallam) missed the optional night Salat (Tahajjud) due to pain or any other reason, he would perform twelve Rak`ah during the day time.