Fiqh-us-Sunnah Volume 5, Hajj and ‘Umrah, Fiqh 5.116.

A pilgrim may shave or cut his hair short right after throwing the first pebbles at Jamarah Al-Aqabah on the Day of Nahr – the 10th of Zhul-Hijjah. If, however, a pilgrim has with him animals to be slaughtered then he can shave or cut his hair short only after having slaughtered these animals.

In a hadith reported by Ma’mar bin Abdullah we read that the Prophet (peace be upon him) slaughtered his sacrificial animal at Mina and said, “He has commanded me to shave (my head).” This was reported by Ahmad and At-Tabarani.

The time to shave or cut one’s hair short while performing ‘Umrah is right after completing Sa’i – seven rounds – between Safa and Marwah. As for those who bring their sacrifical animals with them, they may shave right after they slaughter them.

At the time of shaving or cutting one’ s hair short, according to Abu Hanifah and Malik, one must be in Haram (within the prencincts of the Sacred Mosque) and it must be during the Days of Nahrm – 10th, 11th, 12th and 13th of Zhul-Hijjah. A narration from Ahmad, based on the above hadith, supports this opinion.

Ash-Shafi’i, Mohammad bin Al-Hasan, and, according to his well known position, Ahmad, are of the view that shaving or cutting of one’s hair short must be done within the Sacred Precincts of the Haram, but not necessarily during the Days of Nahr. If one delays shaving one’s head until after these days one may do so without any harm or incurring any penalty.