We should refer to the books of religious jurisprudence to...
We should refer to the books of religious jurisprudence to answer questions such as: 'Are these two Suras the same in every respect' or, 'should we consider them as one Surah in prayers?'. In any case, the consensus of scholars agrees that, in prayers, we cannot recite merely one of the two Suras.
“And soon your lord will grant you, and you shall be well-pleased.” The Occasion of Revelation Many narrations have been cited about the occasion of revelation of this Surah, of which the following is the most clear: Ibn-Abbas says that fifteen days had passed since the Prophet (S) had received any revelation. During this time, the pagans of Mecca taunted Muhammad and said that his Lord had forsaken him and was displeased with him.
They added that if he had been right about his divine mission, the revelation would not have ceased for him. Then, the aforementioned Surah descended (and put an end to their statements).
It is noteworthy that when this Surah was revealed, according to a tradition, the holy Prophet (S) told Gabriel: "You delayed while I was looking forward to seeing you.” And then Gabriel answered him: "I was more eager than you, but I am a missionary servant and do not descend unless by my Lord's leave.” Another tradition cites that a number of Jews came to the Prophet (S) and asked him some questions about the stories of Zul-qarnain, the men of the cave, and the creation of the Spirit.
He told them that he would inform them the next day, but he did not add to his statement: "If Allah wills". This caused the inspiration to cease for a length of time and consequently, the enemies began talking and jearing at him. Hence, the Prophet (S) felt sad and lonely, but later this Surah was revealed to comfort him.
(This occasion of revelation does not seem so fitting since the Jews and their meeting with the Prophet (S), as well as these kinds of questions, usually occurred in Medina, not Mecca).