Musannaf Ibn Abi Shayba 3:4250

Waki’ narrated to us, from Sufyan, from Muhammad ibn ‘Abd al-Rahman, the freed slave of the family of Talhah, from Abu Salamah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) used to perform the taslim after every two rak'ahs of the night prayer.