Musannaf Ibn Abi Shayba 17:1097

Kathir ibn Hisham narrated to us, he said: al-Furat ibn Sulayman narrated to us, from Abd al-Karim, from Ziyad ibn Abi Maryam, who said: Sa'd ibn Abi Waqqas went out on a journey. He said: The gazelles came toward him, and when they drew near to him, they turned back. A man said to him, "O Amir, turn back." Sa'd said to him, "Inform me, from which of them did you take an omen? From their horns when they approached, or from their tails when they turned away?" Then Sa'd said at that: "Indeed, taking omens is a branch of shirk (polytheism)."