Shaving Head in Islam
Question

Is t sunnah to shave the head?
Praise be to Allah.What may be understood from the words of the scholars (may Allah have mercy on them) is that shaving the head is of six kinds: 
1 – An act of worship and a means of drawing closer to Allah, for which a person will be rewarded. This applies in four cases only, to which there is no fifth: 
(i)Hajj
(ii)‘Umrah. Allah says (interpretation of the meaning):
“Indeed Allah shall fulfil the true vision which He showed to His Messenger [i.e. the Prophet saw a dream that he has entered Makkah along with his Companions, having their (head) hair shaved and cut short] in very truth. Certainly, you shall enter Al-Masjid Al-Haraam, if Allah wills,  secure, (some) having your heads shaved, and (some) having your head hair cut short” [al-Fath 48:27]
(iii)Shaving the child’s head on the seventh day after birth. The evidence for that is the hadeeth narrated by al-Tirmidhi (1439) from ‘Ali ibn Abi Taalib (may Allah be pleased with him) who said: “The Messenger of Allah (peace and blessings of Allah be upon him) offered a sheep as ‘aqeeqah for al-Hasan, and said: ‘O Faatimah, shave his head and give the weight of his hair in silver in charity.’” (Classed as hasan by al-Albaani in Saheeh al-Tirmidhi, 1226. See also Tuhfat al-Mawlood by Ibn al-Qayyim, p. 217).
(iv)The kaafir when he becomes a Muslim, because of the report narrated by Abu Dawood (356) which says that the Prophet (peace and blessings of Allah be upon him) commanded a kaafir man who had become Muslim, “Shave off the hair of kufr and get circumcised.” (Classed as hasan by al-Albaani in Saheeh Abi Dawood; see also al-Mughni, 1/276; Sharh al-‘Umdah by Shaykh al-Islam, 1/350)
The scholars (may Allah have mercy on them) were agreed that it is not recommended to shave the head at times other than these four. See al-Istiqaamah by Shaykh al-Islam, 1/256. 
2 – Shirk (the association of others with Allah). Shaving the head may be a form of shirk, when the head is shaved as an act of humbling oneself  before someone other than Allah. Ibn al-Qayyim (may Allah have mercy on him) said in Zaad al-Ma’aad (4/195): “Such as when the mureeds (disciples of Sufi shaykhs) shave their heads for their shaykhs, and one of them says, ‘I shaved my head for So and so.’ This is like saying, ‘I prostrated to So and so,’ because shaving the head is an act of humility and submission, which is why it is one of the acts that complete the Hajj, for it means putting one’s forelock in the hand of its Lord, in submission to His greatness and humbling oneself before His glory. It is one of the most eloquent forms of submission. Hence when the Arabs wanted to humiliate their prisoners and free them, they would shave their heads and let them go…” 
3 – A reprehensible innovation (bid’ah) – this takes many forms, such as: 
Shaving the head as an act of worship and religious devotion – other than in the four cases mentioned above – such as making a shaved  head a sign of righteousness or complete asceticism (zuhd). This is what the Khawaarij used to do. Hence it was narrated that the Prophet (peace and blessings of Allah be upon him) described the Khawaarij as “their sign will be that they shave their heads.” (al-Bukhaari, 7007; Muslim, 1763). Al-Qurtubi said: “ ‘Their sign will be that they shave their heads’ means that they will make that a symbol of their rejection of worldly adornments and a sign by which they might be known. This is ignorance on their part… and introducing something into the religion of Allah which differs from that which the Prophet (peace and blessings of Allah be upon him), the Rightly-guided Khaleefahs and their followers used to do.” (See Sharh al-‘Umdah, 1/231; Majmoo’ al-Fatawa, 21/118). 
Another example is that which some people do, ordering a person who has repented to shave his head. This is a bid’ah (innovation) which was not done by any of the Sahaabah or those who followed them in truth, or by any of the imams of the Muslims. (Majmoo’ al-Fatawa, 21/118) 
4 – Haraam kinds of shaving the head, which takes a number of forms, such as: 
(i)Shaving the head when calamity strikes, such as the death of a relative and the like. It was narrated that Abu Moosa al-Ash’ari (may Allah be pleased with him) said: “The Messenger of Allah (peace and blessings of Allah be upon him) disowned the woman who raises her voice in lament, the one who shaves her hair at times of calamity and the one who rends her garment.” Ibn Hajar (may Allah have mercy on him) mentioned in al-Zawaajir ‘an Iqtiraaf al-Kabaa’ir the 117th major sin: shaving the head at times of calamity. He said: “Because that is showing discontent and a lack of acceptance of the divine decree.”
(ii)Shaving the head in a manner that resembles the kuffaar or immoral people who are well known for shaving their heads. A person might do that as a kind of adornment, to make himself look like them, or he might shave the hair at the sides of the head and leave the middle long. All of these are haraam forms of imitating others, and a form of promiscuity and decadence – we ask Allah to keep us safe and sound. And the Prophet (peace and blessings of Allah be upon him) said: “Whoever imitates a people is one of them.” (Narrated by Abu Dawood, 4031; classed as saheeh by al-Albaani in Saheeh Abi Dawood, 3401). Al-Faari (may Allah have mercy on him) said: i.e., whoever makes himself resemble the kuffaar or immoral people, then he is one of them, i.e., he shares the sin with them.
5 – Permissible – i.e., shaving the head for a reason, such as shaving it as a remedy for disease, or to prevent lice and so on. Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said: This is permissible according to the Qur’aan and Sunnah, and scholarly consensus. (Majmoo’ al-Fatawa, 12/117) 
6 – Shaving the head for none of the reasons stated above. 
This is a matter concerning which the scholars differed. Some of them regarded it as makrooh, such as Maalik (may Allah have mercy on him), and they quoted as evidence the fact that it is the sign of the followers of innovation, namely the Khawaarij, as stated in the hadeeth quoted above. And the Prophet (peace and blessings of Allah be upon him) said: “Whoever imitates a people is one of them.” 
Those who regard it as permissible quoted as evidence the report narrated by Abu Dawood (4192) who said that the Prophet (peace and blessings of Allah be upon him) came to the family of Ja’far ibn Abi Taalib (may Allah be pleased with him) three days after Ja’far had died, and called for a barber and told him to shave the heads of his sons. (Classed as saheeh by al-Albaani in Saheeh Abi Dawood, 3532). 
And Abu Dawood narrated (4195) that the Prophet (peace and blessings of Allah be upon him) saw a child who had part of his head shaved and not other parts. He said: “Shave it all or leave it all.” (Classed as saheeh by al-Albaani in Saheeh Abi Dawood, 3535). Al-Nawawi (may Allah have mercy on him) said: “This clearly shows that it is permissible to shave the head, and it cannot be interpreted in any other way.” (Sharh Muslim). But using these two hadeeth to show that it is permissible to shave the head for no reason is a matter which is subject to further discussion. 
Firstly, shaving the head here is for a reason, so it is permissible, the reason being that boys are more likely than others to be affected by lice, because they sweat a lot and get dirty. Zaad al-Ma’aad, 4/159. 
Secondly, this has to do with a young boy, and concessions are made for children that are not made for adults. Haashiyat al-Sindi ‘ala al-Nasaa’i. See also Majmoo’ al-Fatawa, 21/119; Sharh al-‘Umdah, 1/230. 
There is some difference of opinion concerning the fifth type: is shaving the head makrooh or permissible? It is preferable not to shave it. Al-Faawi (may Allah have mercy on him) said: It is better not to shave it unless that is for Hajj or ‘Umrah, as was the practice of the Prophet (peace and blessings of Allah be upon him) and his companions (may Allah be pleased with them). (From ‘Awn al-Ma’bood, 11/248).
And Allah knows best.