The hair on the head of the new-born must be shaved on the seventh day. It is mustahib (desirable) to give silver in sadaqah to the poor and needy equal to the weight of his or her hair. Shaving the hair of the head provides the child with strength and opens up the pores of the skin. It is also beneficial to the eye-sight, the hearing and the sense of smell. Thereby the poor is helped, too. Sayyidah Fatimah (Radhiallaho Anha) distributed silver as sadaqah equal in weight to the hair on the heads of Sayyidna Hasan Husain Zainab, and umme Kulthum. (Malik in Muwatta and Yahya bin Bukair) on the birth of Sayyidna Hasan, the Noble Prophet,(Sallallaho alaihe Wasallam) asked Sayyidah Fatimah (Radhiallaho Anha) to have his head shaved off and offer silver equal in weight to the hair as sadaqah. The hair weighed a dirham or a little lesser than a dirham. (ibn Ishaq)
The entire head must be shaved. To shave some hair and to leave some on the head is called qaz’ and is disallowed.(Bukhari and Muslim) This is not fair with the head because some of it is bared and the rest hidden. It is exactly as though a part of the body receives sunlight and rest of it is in shade. Also, it may be compared with a shoe on one foot and none on the other. Both these things are forbidden. The intention is to prevent the defacing of one’s appearance. It also aims at discouraging the adoption of unreasonable pretense or resemblance to non-Muslims. You must act on these mustahib deeds so that it is then easy to act on the fard (compulsory deeds).