Sayyidah Hafsah bint Umar (may Allah be pleased with her) relates that when the Messenger of Allah (peace and blessings be upon him) ordered his wives to come out of ihram by means of Umrah, we said: O Messenger of Allah! What prevents you from coming out of ihram with us? He (peace and blessings be upon him) said: "I have sent a sacrificial animal and matted my hair (talbid), so I will not come out of ihram until I have slaughtered."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19619