Musnad Abu Ya'la al-Mawsili 6:31

Zuhayr narrated to us, Muhammad ibn Abdullah al-Asadi narrated to us, Isra'il narrated to us, from Abu Ishaq, from Mus'ab ibn Sa'd, from his father, who said: I swore by al-Lat and al-'Uzza. My companions said to me, "You have spoken nonsense." So I came to the Prophet, may Allah bless him and grant him peace, and said, "O Messenger of Allah, I am a recent convert to Islam, and I swore by al-Lat and al-'Uzza." He said, "Say 'There is no god but Allah' three times, and spit to your left three times, and seek refuge from the Shaytan, and do not do it again."