To end the state of Ihraam, one is required to shave or shorten his hair. I would like to ask the following relevant questions:
1- Is the head hair meant only? Or does the command include hair of other bodily parts? Is the evidence behind specifying the head hair the verse in which Allaah The Exalted Says (what means): {with your heads shaved and [hair] shortened.} [Quran 48: 27]
2- In case of shortening, is one required to shorten the whole head hair or is shortening only three hairs enough? If shortening three hairs will be enough, is it a condition to do so from the origin of the hair or this can be done from any part of it?
3- Is shortening hair permissible only for those who have an excuse not to shave, or is it permissible to do so even without an excuse?Would you please answer these questions in details in case of both men and women.

All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

The required shaving or shortening to end the state of Ihraam is specific to the head hair. According to the consensus of the scholars, hair of other bodily parts is not included. Allaah The Exalted Says (what means):

•        {With your heads shaved and [hair] shortened.}[Quran 48: 27]

•        {And do not shave your heads until the sacrificial animal has reached its place of slaughter.}[Quran 2: 196]

The Messenger of Allaah, sallallaahu ‘alayhi wa sallam, shaved his head during the course of Hajj and said: "Take your rituals (for Hajj) from me."

There is a difference in opinion among scholars regarding the extent that should be shaved or shortened of the head hair. An-Nawawi stated the relevant different opinions and said:

We (Shaafi‘i scholars) have mentioned that it is obligatory to shave or shorten only three hairs. This is also the view of Abu Thawr. Maalik and Ahmad are of the view that it is obligatory to shave or shorten most of the head hair. Abu Haneefah is of the view that one fourth of the head hair is due. Abu Yoosuf is of the view that one half is due. They quoted the action of the Prophet, sallallaahu ‘alayhi wa sallam, as he shaved his whole head and said in a Saheeh Hadeeth: "Take your rituals (for Hajj) from me."  They also argued that one's hair is not deemed shaved unless most of it is shaved. The Shaafi‘i scholars quoted the verse in which Allaah The Exalted Says (what means): {with your heads shaved and [hair] shortened.}[Quran 48: 27] The verse means the head hair, and the minimum is to shave three hairs. It is possible to say that so and so shaved his whole head, one fourth of it or three hairs. As for the action of the Prophet, sallallaahu ‘alayhi wa sallam, we are of the view that this is recommended and that shaving the whole head is not obligatory."

Although the Shaafi‘i scholars as well as another group of scholars are of the view that shaving three hairs will be enough for freeing the liability, there is no doubt that it is more cautious to follow the view of Maalik and Ahmad who said that it is obligatory to shave or shorten most of the head hair.

Shortening is permissible for those who have an excuse not to shave and those who do not have an excuse. However, shaving is better, but not for a pilgrim who performs the Tamattu‘ Hajj after ending the state of Ihraam for ‘Umrah. As evidence, Allaah The Exalted Says (what means): {with your heads shaved and [hair] shortened.}[Quran 48: 27]

Moreover, the Prophet, sallallaahu ‘alayhi wa sallam, supplicated thrice in favor of those who shave and only once in favor of those who shorten. This indicates that shortening is permissible in all cases even if there is no excuse and that shaving is better, as we clarified.

As for the woman, according to the scholars' consensus, she is not required to shave. Rather, it is recommended for her to shorten most of her hair according to the scholars who maintain the view that shortening three hairs is sufficient for freeing the liability. According to Maalik and Ahmad she is obliged to do so.

An-Nawawi said:

Ibn Al-Munthir said: the scholars unanimously agree that women are not required to shave. Rather, they are required just to shorten. They also said that it is disliked for women to shave for this is an innovation in religion if done by women and it also involves disfigurement. The scholars provided different views regarding the extent that should be shortened. Ibn ‘Umar, Ash-Shaafi‘i, Ahmad, Is-haaq and Abu Thawr are of the view that she should shorten the length of a fingertip from each part of the head hair.