It is narrated from Hazrat Aisha (may Allah be pleased with her) that when the Prophet (peace and blessings be upon him) would enter the morning, he would perform two short rak'ahs, then lie down on his right side.
Hadith Referenceمسند احمد / مسند النساء / 24217
Hadith Gradingحکم دارالسلام:حديث صحيح، وهذا إسناد حسن لأجل عبدالرحمن بن إسحاق فإنه حسن الحديث