The Messenger of Allah ﷺ used to pray eleven units of prayer after the evening prayer. When morning came, he would pray two brief units, then lie down on his right side until the caller to prayer came to inform him that the prayer was due.
حدثنا عبد الأعلى عن معمر عن الزهري عن عروة بن الزبير
كان رسول الله ﷺ يصلي بعد العشاء إحدى عشرة ركعة فإذا أصبح صلى ركعتين خفيفتين ثم اضطجع على شقه الأيمن حتى يأتيه المؤذن فيؤذنه بالصلاة
Its isnad is sahih. It is found in Bukhari 2/109 no. 626 in the chapter on the adhan, Muslim 1/508 no. 736 in the chapter on travelers, Abu Dawud 2/38 no. 1335, Nasai 3/243 no. 1726, Ibn Majah 1/432 no. 1358, and Darimi 1/400 no. 1447.