Allah's Messenger (ﷺ) slaughtered (the Hadi) before he had his head shaved and then he ordered his Companions to do the same.
Sahih al-Bukhari Book 27, Hadith 6
← Previous Hadith (Abdullah) bin `Umar used to say, "Is not (the following of) the tradition of Allah's Messenger (ﷺ) sufficient for you? If anyone of you is prevented from performing Hajj, he should perform the Tawaf of the Ka`ba and between As-Safa and Al-Marwa and then finish the Ihram and everything will become legal for him which was illegal for him (during the state of Ihram) and he can perform Hajj in a following year and he should slaughter a Hadi or fast in case he cannot afford the Hadi."

Sahih al-Bukhari Book 27, Hadith 5 Next Hadith → That `Abdullah and Salim said to `Abdullah bin `Umar, "(You should not go for Hajj this year)." `Abdullah bin `Umar replied, "We set out with the Prophet (to Mecca for performing `Umra) and the infidels of Quraish prevented us from reaching the Ka`ba. Allah's Messenger (ﷺ) slaughtered his Budn (camels for sacrifice) and got his head shaved."

Sahih al-Bukhari Book 27, Hadith 7