Fourth: In the first rak‘ah, one should recite: “Say, O disbelievers” [Surah al-Kafirun], and in the second: “Say, He is Allah, the One” [Surah al-Ikhlas] (1). Alternatively, one may recite in the first: “Say, ‘We believe in Allah’” [Surah al-Baqarah 2:136]—the verse in Surah al-Baqarah—and: “Say, ‘O People of the Book, come to a word that is common between us’” [Surah Al ‘Imran 3:52]—the verse in Surah Al ‘Imran—in the second (2). Thus, one may sometimes recite Surah al-Ikhlas and Surah al-Kafirun, and at other times the verses from Surah al-Baqarah and Surah Al ‘Imran. If you have not memorized the verses from Surah al-Baqarah and Surah Al ‘Imran, then recite Surah al-Ikhlas and Surah al-Kafirun.
Fifth: It is sunnah, after these two rak‘ahs, to lie down on one’s right side. The scholars have differed regarding this lying down:
Some have said that it is not sunnah at all.
Others have said that it is sunnah in all cases.
Others have said that it is sunnah for one who prays at night, because he needs rest in order to be refreshed for the Fajr prayer.
Others have said that it is a condition for the validity of the Fajr prayer, and that whoever does not lie down after the two rak‘ahs has an invalid Fajr prayer. This was the view held by Ibn Hazm (may Allah have mercy on him). He said: The Prophet ﷺ said, “When one of you has prayed the two rak‘ahs of Fajr, let him lie down after them” (3). Thus, he commanded that one lie down. However, the response to this is as follows: