Musnad Ahmad 588:2

'Abd al-Razzaq narrated to us, Ma'mar informed us, from Qatadah, from Sinan ibn Salamah, from Ibn 'Abbas, that Dhu'ayb informed him that the Prophet (peace and blessings of Allah be upon him) sent two sacrificial camels with him, and commanded him: "If anything happens to them, or if they become incapacitated, then slaughter them, then dip their sandals in their blood, then strike the side of each one with its sandal, and leave them for the people, and neither he nor any of his companions shall eat from them." 'Abd al-Razzaq said: He used to narrate it as a *mursal* report, meaning Ma'mar, from Qatadah. Then I wrote it for him from the book of Sa'id, so I gave it to him, and he looked and read it, then said: "Yes, but I am hesitant when I do not look at the book."