Musannaf Ibn Abi Shayba 34:265

Al-Fadl narrated to us, Sufyan narrated to us, Ja’far narrated to us, from his father, that he used to consider it recommended to recite in the two rak’ahs [performed] upon first arriving [at the Ka’bah], "Say, 'O disbelievers,'" and "Say, 'He is Allah, [who is] One,'" during the tawaf.