Musnad Ahmad 1034:153

Abu Nu'aym narrated to us, Mis'ar narrated to us, from Abu Bakr ibn 'Amr ibn 'Utbah, from Ibn Hudhayfah—Mis'ar said: And he mentioned it once from Hudhayfah—that: "The prayer of the Messenger of Allah, peace and blessings of Allah be upon him, would indeed be reached by a man, his child, and his child's child."