Musnad Ahmad 33:121

Waki’ narrated to us, al-A’mash narrated to us, from Abu Sufyan, from Jabir, who said: The Prophet, peace and blessings of Allah be upon him, was asked: "Which Jihad is best?" He said: "He whose horse is hamstrung and his blood is spilled." He said: And he was asked: "Which prayer is best?" He said: "The long standing (Qunut)."