It is permissible to use the hair from a pig in a comb because the strongest opinion is that it is pure.
Shaikhul Islam Ibn Taymiyyah (may Allah have mercy upon him) said: “The most correct opinion is the purity of all hairs: dogs or pigs and other than them, unlike [their] saliva. Based on this, if the hair of a dog is wet and it touches the cloth of a person, then there is not anything upon him as is the mathahb of the majority of the jurists: Abu Hanifa, Malik, and Ahmad in one of the two reports from him. That is because the origin of things is permissibility and it is not allowed to declare something impure nor make it unlawful without an evidence as He, the Exalted said:
وَقَدْ فَصَّلَ لَكُمْ مَا حَرَّمَ عَلَيْكُمْ إِلَّا مَا اضْطُرِرْتُمْ إِلَيْهِ
While He has explained to you in detail what is forbidden to you, except under compulsion of necessity? [6:119]
And:
وَمَا كَانَ اللَّهُ لِيُضِلَّ قَوْمًا بَعْدَ إِذْ هَدَاهُمْ حَتَّى يُبَيِّنَ لَهُمْ مَا يَتَّقُونَ
And Allah will never lead a people astray after He has guided them until He makes clear to them as to what they should avoid [9:115]
The Prophet (ﷺ) in the Saheeh Hadith:
أَعْظَمُ الْمُسْلِمِينَ فِي الْمُسْلِمِينَ جُرْمًا مَنْ سَأَلَ عَنْ أَمْرٍ لَمْ يُحَرَّمْ فَحُرِّمَ عَلَى النَّاسِ مِنْ أَجْلِ مَسْأَلَتِهِ
The greatest sinner of the Muslims amongst Muslims is one who asked about a certain thing which had not been prohibited and it was prohibited because of his asking about it [Saheeh Muslim no. 2358]
And in the Sunan from Salman (may Allah be pleased with him) marfoo’ and some have made it Mawqoof that he said:
الْحَلاَلُ مَا أَحَلَّ اللَّهُ فِي كِتَابِهِ وَالْحَرَامُ مَا حَرَّمَ اللَّهُ فِي كِتَابِهِ وَمَا سَكَتَ عَنْهُ فَهُوَ مِمَّا عَفَا عَنْهُ
What is lawful is that which Allah has permitted, in His Book and what is unlawful is that which Allah has forbidden in His Book. What He remained silent about is what is pardoned [Saheeh Ibn Majah no. 2731]
[Majmoo’ Fatawa (21/617)]
Translated by
Faisal bin Abdul Qaadir bin Hassan
Abu Sulaymaan