Musnad Ahmad 22:33

Hammad ibn Khalid narrated to us, he said: Ibn 'Allathah narrated to us, from Maslamah al-Juhani, he said: I heard him narrating from al-Fadl ibn 'Abbas, he said: I went out with the Messenger of Allah, peace and blessings of Allah be upon him, one day, and a gazelle darted across. It inclined toward his side, so I embraced it. I said: "O Messenger of Allah, have I taken an omen?" He said: "The omen is only that which makes you proceed or turns you back."