Musannaf Ibn Abi Shayba 3:5969

Abu Muhammad Abdullah ibn Yunus narrated to us, Baqi ibn Makhlad (may Allah have mercy on him) narrated to us, he said: Abu Bakr narrated to us, he said: Waki’ narrated to us, from al-A’mash, from Abu Sufyan, from Jabir, who said: The Messenger of Allah (peace and blessings of Allah be upon him) was asked: "Which prayer is best?" He said: "The length of the Qunut (standing)."