It is the fifth obligation in Umrat-ut-Tamatu'. What is in sa'y is that it must be embarked on with the niyyah of alqurbah. It is materialized by cutting some hair of the head, beard or moustache.
Evidently (al adhhar), it is not enough for taqseer to be recognized as valid that one merely plucks out hair. As it is widely held (alal mashhoor), it be accepted by cutting the nails of hand or foot, as an alternative. However it should, as a matter of precaution (alal ahwat), not be performed independent of cutting the hair first.
Rule 350: Taqseer has to be done when coming out of Umrat-ut-Tamatu'. It is not permissible to shave the head, as doing so is forbidden; it attracts a kaffarah of a sheep, if one does so knowingly and deliberately. Indeed, this could be the case in all circumstances, as a matter of recommended precaution (al ahwatil aqwa).
Rule 351: If a pilgrim, knowingly and deliberately, engage in a sexual act after sa'y, but before taqseer, he is liable to bear a kaffarah of a camel, as has been discussed under Ihram. However, if he did so in ignorance of the rule, he should be relieved of the penalty.
Rule 352: Taqseer must follow sa'y, i.e. it is not permissible to perform it before sa'y.
Rule 353: Taqseer is not obligatory immediately after sa'y. It is permissible to do taqseer wherever one pleases, whether at sa'y place, at one's house, or at any other venue.
Rule 354: If a pilgrim deliberately fails to do taqseer, and subsequently wears ihram for Hajj, his Umrah is invalidated. Evidently, his Hajj changes to Ifraad. He must perform Umrat-ul-Mufradah later. He should, as a matter of precaution, repeat the Hajj in the following year.
Rule 355: If a pilgrim fails to do taqseer, due to an oversight, and subsequently wears ihram for Hajj, his Umrah and ihram are valid. However he must, as a matter of recommended precaution, pay a kaffarah of a sheep.
Rule 356: When a pilgrim, in Umrat-ut-Tamatu', performs taqseer, all the prohibitions, imposed while in a state of ihram, are lifted, including shaving the head. However, as a matter of precaution, it is lawful to shave the head within thirty days from the day of Eid-ul-Fitr, but not after that period. If he deliberately does shave after the period, he must, as a matter of precaution, pay a kaffarah of a sheep.
Rule 357: In Umrat-ut-Tamatu', Tawaf-un-Nisa is not obligatory; yet there is no objection to performing it.