Musnad Ahmad 5:707

Mu'awiyah ibn Hisham narrated to us, Sufyan narrated to us, from Salim ibn Abi Hafsah, who said: It reached me from Abdullah ibn Mulayl, so I went to him early in the morning and found them at a funeral. A man narrated to me, from Abdullah ibn Mulayl, who said: I heard Ali saying: "Every prophet was given seven noble ones (nujaba'), and your prophet was given fourteen noble ones, among them: Abu Bakr, Umar, Abdullah ibn Mas'ud, and Ammar ibn Yasir."