Musnad Ahmad 799:117

'Affan narrated to us, Aban al-'Attar narrated to us, Qatadah narrated to us, from al-Hasan, from Samurah, from the Prophet (peace be upon him), the like of it, except that he said: "And it is named (yusamma)." Hammam said in his narration, and we reviewed it with him: "And it is stained with blood (yudma)." Hammam said: Qatadah used to describe the blood, saying: "When the 'Aqiqah is slaughtered, a tuft of wool is taken and placed against the jugular veins of the slaughtered animal, then it is placed on the crown of the infant's head. When it drips, his head is washed, and then he is shaved afterwards."