292 – Abu Hurayrah (may Allah be pleased with him) reported: “The Prophet ﷺ recited in the two rakʿahs before Fajr, ‘Say: O disbelievers’ (Q 109) and ‘Say: He is Allah, the One’ (Q 112).” Muslim narrated it. (1)

293 – ʿĀʾishah (may Allah be pleased with her) said: “When the Prophet ﷺ had performed the two rakʿahs before Fajr, he would lie down on his right side.” Al-Bukhārī recorded it. (2)

Vocabulary of Ḥadith 293:
– iḍṭajaʿa: from the root ḍ-j-ʿ, “to lie down.” It is originally on the pattern iftaʿala, but some Arabs change the tāʾ into ṭāʾ and pronounce it before the ḍād, saying iḍṭajaʿ; others change the tāʾ to ḍād and assimilate it into the ḍād, saying iḍjaʿ, giving precedence to the original consonant, the ḍād.
– shiqquh al-ayman: with a kasrah on the shīn and a doubled qāf; it means “his right flank,” the area from under the armpit down to the waist.

As for the reason the right side is specified—and Allah knows best, as al-Karmānī observed—it is so that one does not slip into deep sleep. The heart is on the left side; when a person lies on the right, the heart remains somewhat suspended and unsettled, whereas lying on the left brings comfort and ease, making deep sleep more likely.