I'm not sure it can be concluded from 17:79 that night prayer was a mandate on the Prophet (PBUH). The word نافلة means an extra. That does not imply a mandate.
لسان العرب says النافِلة ما كان زيادة على الأَصل so the night prayer in 17:79 could be a mandate under the interpretation that the 'extra' aspect here is that the Prophet (PBUH) has to do it while others don't have to.
That is one of the arguments quoted by Ar-Raazi, in his book مفاتيح الغيب, volume 15, page 795, as evidence that the command in 73:2 was a recommendation and not a mandate. He quotes two other arguments:
- If standing up at night in prayer were a mandate on the Prophet (PBUH), then it would have been a mandate on his followers too, because God orders Muslims to follow the Prophet (PBUH), e.g.,
Ar-Raazi seems to agree with this argument.
- The options stated in 73:2-4 mean it's not a mandate because letting the person decide implies no mandate. `Ataaya agrees but Ar-Raazi doesn't. His argument is that the mandate may be the standing up at night in prayer but for how long, it's up to the worshiper. I agree that this is a valid refutation of this particular argument.
`Ataaya makes a very interesting point: that the clause "He knew you would not hold it" (73:20) refers to the Quran
, not to the prayer, evidenced by the very next clause, "Therefore, recite what you can of the Quran." Thus, if any amendment is mentioned in 73:20 is to make clear that 73:1-4 did not mean to recite the entire Quran every night! Only whatever portion of it the worshiper is able to recite.
`Ataaya also agrees with me
that the phrase فتاب عليكم
means that God acknowledged the extra burden you've put on yourselves and relieves you of it, proving again that they were not commanded to do it.
Al-Khazraji, in his book نفس الصباح في غريب القرآن وناسخه ومنسوخه, volume 2, page 758, mentions two more opinions about the abrogating,
- Ibn Kuzayma said that what abrogated 73:1-2 is 73:3 which is something I wondered why no scholar has mentioned.
Ar-Raazi opined, like I did, that 73:2-4 give options to the Prophet (PBUH), not that any one option abrogates the others.