Dying grey hair of the beard or hair is sunnah and part of Islam. However a person must not dye their beard nor hair black.

It was narrated that Abu Hurayrah (may Allah be pleased with him) said: The Prophet (blessings and peace of Allah be upon him) said: “The Jews and Christians do not dye their hair, so be different from them.”

Narrated by al-Bukhari (5899).

It was narrated that Jaabir ibn ‘Abdullah said: Abu Quhaafah was brought on the day of the Conquest of Makkah, and his hair and beard were white like hyssop. The Messenger of Allah (blessings and peace of Allah be upon him) said: “Change this with something, but avoid black.” Narrated by Muslim (2102). 

An-Nawawi (may Allah have mercy on him) said:

With regard to hyssop … Abu ‘Ubayd said: It is a plant with white flowers and fruits; the whiteness of his hair was likened to it. Ibn al-A‘raabi said: It is a plant that is white, as if it were salt. 

Abu Quhaafah’s name was ‘Uthmaan; he was the father of Abu Bakr as-Siddeeq. He became Muslim on the day of the conquest of Makkah.

End quote from Sharh Saheeh Muslim (14/79-80) 

Ibn `Abbas (may Allah be pleased with him) said: “The Messenger of Allah (Peace and Blessings of Allah be upon Him) said: `At the end of time there will be people who will dye their hair black like the crops of pigeons. They will never even smell the fragrance of Paradise.” (Narrated by Ahmad; see also Sahih Al-Jami`, 8153)

 Prophet (peace and blessings of Allah be upon him) said: “Change grey hairs and do not be like the Jews.” Narrated by al-Nasai, 4986; al-Tirmidhi, 1674. 

It was narrated by Muslim (3924) that when the Prophet (peace and blessings of Allah be upon him) saw grey hair on the head of Abu Bakr’s father, he said: “Change this with something.” According to al-Bukhari (5448) he said: “The Jews do not dye their hair, so be different from them.” 

It was also reported from the Prophet (Peace and Blessings of Allah be upon Him) that one should change grey hair, using any colour except black . Abu Dharr (may Allah be pleased with him) reported that the Prophet (Peace and Blessings of Allah be upon Him) said: “The best things with which to change grey hair are henna and ‘katam’ (a plant similar to henna which is used as a dye).” (Narrated by At-Tirmidhi, 1675; he said: This is an authentic Hadith).

In a hadith narrated by Abu Dawud (4212) from Ibn ‘Abbas who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: “There will be people at the end of time who will dye their hair black like the crops of birds; they will never smell the fragrance of Paradise.” This hadith was classed as sahih by al-Albani in Sahih Abi Dawud.

The fact that it is permissible to dye the hair red and yellow was narrated by Abu Dawud (4211) from Ibn ‘Abbas who said: A man who had dyed his hair with henna passed by the Prophet (peace and blessings of Allah be upon him) and he said: “How handsome this is.” Then another who had dyed his hair with henna and katam passed by and he said, “This is more handsome.” Then another who had dyed his hair yellow passed by and he said: “This one is more handsome than all the others.” The comments in this hadith had to do with changing grey hairs to another colour, not to dyeing the hair in all cases even if it is not grey. 

Al-Albani said concerning this hadith in Mishkat al-Masabih: it is jayyid (good). 

Shaykh Muhammad ibn ‘Uthaymeen (may Allaah have mercy on him) said: 

The Sunnah is to change the grey hairs by using henna, or henna and katam. If it is changed using henna it will be orange and if it is changed using henna and katam it will be between red and black. There is nothing wrong with that and no sin involved, in sha Allah. (end of quote)

It was narrated from ‘Amr ibn ‘Abasah that the Messenger of Allah (blessings and peace of Allah be upon him) said: “If one hair of a person turns white in Allah’s cause, it will be light for him on the Day of Resurrection.” Narrated by at-Tirmidhi (1635); he said: This is a hasan saheeh ghareeb hadith. It was narrated that Shurahbeel ibn as-Simt said: O Ka‘b ibn Murrah, narrate to us something from the Messenger of Allah (blessings and peace of Allah be upon him) and be careful [in narrating]. He said: I heard the Messenger of Allah (blessings and peace of Allah be upon him) say: “If one hair of a person turns white in Islam, it will be light for him on the Day of Resurrection.” Narrated by at-Tirmidhi (1634) and an-Nasaa’i (3144). It was also narrated by an-Nasaa’i in as-Sunan al-Kubra (4/288) and by Imam Ahmad in al-Musnad (29/606) with the words “… turns white in Allah’s cause.”

Based on the report which mentions “in Allah’s cause”, what is meant is the one whose hair turns white because of the difficulty encountered in his striving to do acts of worship. But with regard to the report which mentions turning white “in Islam”, there is a corroborating report to support it.

It was narrated that ‘Umar ibn al-Khattaab (may Allah be pleased with him) said: I heard the Messenger of Allah (blessings and peace of Allah be upon him) say: “If one hair of a person turns white in Islam, it will be light for him on the Day of Resurrection.” Narrated by Ibn Hibbaan (2983). Its isnaad was classed as qawiy (strong) by the commentator on al-Ihsaan, Shaykh Shu‘ayb al-Arna’oot, and it was classed as saheeh by al-Albaani in at-Ta‘leeqaat al-Hisaan (5/21).

At-Teebi (may Allah have mercy on him) said:

“If one hair of a person turns white in Allah’s cause…”

What is meant is: the one who strives hard in worship and obedience to Allah until a patch of his hair turns white will have reward beyond description. This is indicated by the fact that light is singled out for mention and it is mentioned in the indefinite form. Those who narrated the words “in Islam” instead of “in Allah’s cause” meant by using a general word (Islam) something specific (in Allah’s cause), or they called jihaad (striving) Islam, because it is the foundation and pinnacle of Islam. End quote from Sharh al-Mishkaat (8/2669).

In the hadith of ‘Abdullah ibn ‘Amr (may Allah be pleased with him) the Prophet (blessings and peace of Allah be upon him) forbade plucking out white hairs, and he said: “It is the light of the Muslim.” Narrated by Imam Ahmad in al-Musnad (11/550), at-Tirmidhi (4202), and Abu Dawood (4202). At-Tirmidhi said: This is a hasan hadith.

Ibn Hibbaan (2985) narrated from Abu Hurayrah that the Messenger of Allah (blessings and peace of Allah be upon him) said: “Do not pluck out white hairs, for they will be light on the Day of Resurrection. Whoever gets a white hair in Islam, one good deed will be recorded for him because of it, one bad deed will be erased from him because of it, and he will be raised one degree in status because of it.” Its isnaad was classed as hasan by the commentator on al-Ihsaan, Shaykh Shu‘ayb al-Arna’oot, and also by Shaykh al-Albaani in at-Ta‘leeqaat al-Hisaan (5/22-23).

As Muslims must we must look at Islamic issues wholistically and be humble.

Firstly A person must not speculate on matters of the deen thinking how very smart and pious you are and saying I don’t dye my white beard because i want to be natural even when another student of knowledge is suggesting maybe he should dye his hair. Rather he should ask is it sunnah to do this instead of thinking i am so much smarter and i am so pious and knowledable in Islam, so ofcourse whatever i say must be right.

Secoundly a person may have heard of the the hadith of ‘Abdullah ibn ‘Amr (may Allah be pleased with him), according to which the Prophet (blessings and peace of Allah be upon him) forbade plucking out white hairs, and he said: “It is the light of the Muslim.” Narrated by Imam Ahmad in al-Musnad (11/550), at-Tirmidhi (4202), and Abu Dawood (4202).

Then thinking this means white hair cannot be dyed but rather he should do his research and find if there are other hadiths which talk about white/grey hair or dying hair, If we look careful this hadith forbids plucking white hair.