Musannaf Ibn Abi Shayba 33:1345

Ibn Fudayl narrated to us, from his father, from Isma'il, from al-Hasan, who said: When he recited, "The mutual rivalry for piling up [worldly things] diverts you," he said: In wealth and children. "Until you visit the graves. Nay! You shall come to know." He said: A threat after a threat. "The certainty of knowledge."