Musannaf Ibn Abi Shayba 3:4014

Waki’ narrated to us, he said: Sufyan narrated to us, from ‘Ata’ ibn al-Sa’ib, from al-Qasim ibn Abi Ayyub, from Sa’id ibn Jubayr, he said: Do not lie down after the two rak’ahs before the dawn (Fajr), and lie down after the Witr.