Tabarruk (seeking barakah or blessings) from the relics of the Prophet (blessings and peace of Allah be upon him) was something that was done at the time of the Prophet (blessings and peace of Allah be upon him), with things such as water left over from his wudoo’, his garment, his food and drink, his hair, and anything else from him.
As for seeking barakah from anything that had touched his body, such as wudoo’ water, sweat, hair and so on, this is something that was well-known and regarded as permissible by the Sahaabah (may Allah be pleased with them) and those who followed them in truth, because of the goodness and barakah that there is in that, and the Prophet (blessings and peace of Allah be upon him) approved of them doing that.
It says in al-Mawsoo‘ah al-Fiqhiyyah (10/70):
The scholars are unanimously agreed that it is permissible to seek barakah from the relics of the Prophet (blessings and peace of Allah be upon him), and the scholars of seerah (Prophet’s biography), shamaa’il (Prophet’s character) and hadith narrated many reports that speak of the noble Sahaabah (may Allah be pleased with them) seeking barakah from various relics of the Prophet (blessings and peace of Allah be upon him). End quote.
Please see the answer to question no. 10045
Secondly:
This tabarruk (seeking barakah) is not permissible with anything other than the relics of the Prophet (blessings and peace of Allah be upon him). So it is not permissible to draw an analogy with anyone else. Seeking barakah from the relics of anyone else among the righteous is a reprehensible innovation (bid‘ah) and it is a means that leads to shirk.
Ibn ‘Uthaymeen (may Allah have mercy on him) said:
The Sahaabah used to seek barakah from the sweat of the Prophet (blessings and peace of Allah be upon him), and they used to seek barakah from his saliva, and they used to seek barakah from his garment, and they used to seek barakah from his hair. But in the case of anyone other than him (blessings and peace of Allah be upon him), no barakah is to be sought from any of these things. So one cannot seek barakah from a person’s garment, hair, nails or anything else of his, except in the case of the Prophet (blessings and peace of Allah be upon him). End quote.
Sharh Riyaadh as-Saaliheen (4/243)
Thirdly:
There is no proof that any of the relics of the Prophet (blessings and peace of Allah be upon him) exist now. Anyone who claims that any such thing exists has no proof to that effect. Based on that, it is not permissible for anyone to claim to have in his keeping any of the relics of the Prophet (blessings and peace of Allah be upon him), unless he has definitive evidence, and how could he have that?
The great scholar and historian Ahmad Pasha Taymoor said:
There is no valid proof for the hairs that were kept by people after that. Something of that which was shared out among the Companions (may Allah be pleased with them) may have reached them, but it is difficult to know what is genuine and what is not.