The Messenger of Allah ﷺ said, "When one of you has prayed the two units before the dawn prayer, let him lie down on his right side."
حدثنا عفان حدثنا عبد الواحد بن زياد حدثنا سليمان الأعمش عن أبي صالح
قال رسول الله ﷺ إذا صلى أحدكم الركعتين قبل صلاة الصبح فليضطجع على جنبه الأيمن
Its isnad is sahih. Bukhari narrated it with a different wording, 2/70, Book of the Two Eids, Lying on the Right Side, and Tirmidhi, 2/281, no. 420, with the wording of Ahmad, and said, hasan sahih gharib, and Ibn Majah, 1/378, no. 1199.