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 (pbuh) liked that act of worship most in the performance of which a person was regular and constant.  
[muslim].

153. `umar bin al-khattab (may allah be pleased with him) reported: messenger of allah (pbuh) 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''.
[muslim].

commentary: the word `hizb' originally means to take one's turn for getting water from a well. subsequently, people started using it for daily round of recitation which one adopts on his own voluntarily. for instance, fixing a number of nawafil (voluntary prayers), recital of a certain portion of the noble qur'an or performance of some other noble deed as one's daily routine. this hadith stresses that one must adhere to such routine. it also tells that if for some reason one is unable to do it at the time fixed by him, he can do it later at the time closest to the one he has fixed for it. if one does so, he will be eligible to its full reward.

154. `abdullah bin `amr bin al-`as (may allah be pleased with them) reported: messenger of allah (pbuh) 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].

commentary:  the excellence of manners demands that if someone has something reprehensible in his character, the person concerned should not be mentioned but the shortcoming must be indicated so that people refrain from it. the second point that we learn from this hadith is that if one starts a good deed, he should try his best to do it perpetually because its perpetuation is liked by allah.

155.  `aishah (may allah be pleased with her) reported: when messenger of allah (pbuh) missed the optional night salat (tahajjud) due to pain or any other reason, he would perform twelve rak`ah during the day time.
[muslim].

commentary:  the qada' of nawafil (offering prayer to make up for having failed to offer it at their due time) is not binding. but it is mustahab (desirable). the prophet (pbuh) did it.