A man had his hair cut on the tenth of Dhul-Hijjah, forgetting that he will sacrifice. What is the ruling on him?
There is nothing wrong for him, for Allah (Glorified and Exalted be He) describes the believers as saying:
Our Lord! Punish us not if we forget or fall into error
According to a Hadith authentically reported from the Prophet (peace be upon him) that Allah said: "I have done that".
Related by Muslim in his Sahih.
(Part No. 11; Page No. 405) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.