Musnad Abu Ya'la al-Mawsili 1:56

Ishaq ibn Ibrahim narrated to us, Hisham ibn Yusuf narrated to us, from Ibn Jurayj regarding the saying of the Exalted: "Or have they attributed to Allah partners who created like His creation?" (Ar-Ra'd). Layth ibn Abi Sulaym informed me, from Abu Muhammad, from Hudhayfah, from Abu Bakr—either Hudhayfah witnessed that from the Prophet, peace be upon him, or Abu Bakr informed him—that the Prophet, peace be upon him, said: "Shirk (polytheism) among you is more hidden than the crawling of an ant." We said, "O Messenger of Allah, is there any shirk other than what is worshipped besides Allah or what is called upon alongside Allah?"—'Abd al-Malik doubted [the wording]. He said, "May your mother be bereaved of you, O Siddiq! Shirk among you is more hidden than the crawling of an ant. Shall I not inform you of a statement that will remove its small and its large [parts]?" I said, "Yes, O Messenger of Allah." He said, "Say every day three times: 'O Allah, I seek refuge in You from associating anything with You while I know, and I seek Your forgiveness for what I do not know.' And shirk is for one to say, 'Allah and so-and-so gave me,' and the 'nidd' (rival/equal) is for a person to say, 'Had it not been for so-and-so, so-and-so would have killed me.'"