When the treaty of Hudaybiyah was written & finalized, it was the time for returning back to Madinah, so Rasoolullah Sallallaho Alaihe Wasallam had to take off his Ehraam, he entered the Haram (crossing the *Ansaab at Hudaybiyah* ), sacrificed the animal, shaved his head, opened the Ehraam & the Sahaabah did the same, to recall the event, read Seerat-e-Nabawi