When the Messenger of Allah ﷺ stopped to rest at night, he would lie down on his right side, and when he stopped to rest just before dawn, he would prop up his forearms and place his head between his palms.
حدثنا عبد الصمد حدثنا حماد حدثنا حميد عن بكر عن عبد الله بن رباح
أن رسول الله ﷺ كان إذا عرس بليل اضطجع على يمينه وإذا عرس قبل الصبح نصب ذراعيه ووضع رأسه بين كفيه
Its isnad is sahih. It is found in Bukhari 2/109 no. 626 in Fath al-Bari, in the chapter on adhan, in Muslim 1/508 no. 736, in the chapter on travelers, in Nasai 3/30 no. 685, in the chapter on adhan, in Ibn Majah 1/378 no. 1198, and in Malik 1/20 no. 8, in the chapter on night prayer.