Slaughtering before having one's head shaved

Narrated Abu Musa: I came upon Allah's Messenger (ﷺ) when he was at Al-Batha. He asked me, "Have you intended to perform the Hajj?" I replied in the affirmative. He asked, "For what have you assumed lhram?" I replied," I have assumed Ihram with the same intention as that of the Prophet (ﷺ) ." The Prophet (ﷺ) said, "You have done well! Go and perform Tawaf round the Ka`ba and between Safa and Marwa." Then I went to one of the women of Bani Qais and she took out lice from my head. Later, I assumed the Ihram for Hajj. So, I used to give this verdict to the people till the caliphate of `Umar. When I told him about it, he said, "If we take (follow) the Holy Book, then it orders us to complete Hajj and `Umra (Hajj-at- Tamattu`) and if we follow the tradition of Allah's Messenger (ﷺ) then Allah's Messenger (ﷺ) did not finish his lhram till the Hadi had reached its destination (had been slaughtered). (i.e. Hajj-al-Qiran). (See Hadith No. 630)