Praise be to Allah.
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).
But mentioning Islam instead of jihad does not rule out the fact that this is the reward of the one who engages in striving, for he will have an immense light because of his immense effort in striving, whereas other Muslims will have light because of their white hairs, commensurate with their level of faith and commitment to doing righteous deeds. This is supported by the fact that there are other reports which indicate that the light one may gain because of white hairs is for all Muslims, not only for those who strive hard, as in 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). 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).
Al-Mubaarakfoori (may Allah have mercy on him) said:
The words “he forbade plucking out white hairs” refer to white hairs in the beard or on the head. He said: “They will be light for the Muslim,” meaning that this is something that is specific to Muslims, because it is something that adds to the Muslim’s dignity, which prevents conceit and leads to humility, and that will make him lose interest in physical desires and have no energy to pursue them. This in turn leads him to develop the light of righteous deeds, so that they will become light in his grave, and that light will go ahead of him in the darkness of the place of gathering [on the Day of Resurrection].
End quote from Tuhfat al-Ahwadhi (8/88).
The Muslim should pay attention to the fact that stress and worry, and the impact that they have on the Muslim of making him feel vulnerable and causing him to develop white hairs, and so on, are things in which there is something good for the Muslim, by means of which his sins are expiated.
It was narrated from ‘Ata’ ibn Yasaar, from Abu Sa‘eed al-Khudri and from Abu Hurayrah, that the Prophet (blessings and peace of Allah be upon him) said: “No hardship, pain, worry, grief, harm or distress befalls a believer, not even the prick of a thorn, but Allah will expiate some of his bad deeds thereby.” Narrated by al-Bukhaari (5641) and Muslim (2573).
What the Muslim should do is show goodly patience when faced with worries and stress, and what may result from that of white hairs. If he does that, then he is promised an immense reward.
Allah, may He be exalted, says (interpretation of the meaning):
“Indeed, the patient will be given their reward without account”
Shaykh ‘Abd ar-Rahmaan as-Sa‘di (may Allah have mercy on him) said:
This is general in meaning and applies to all types of patience, patience in accepting the painful decrees of Allah without resentment or complaint; patience in keeping away from disobedience towards Allah and refraining from sins; patience in obeying Allah and doing acts of worship. Allah has promised the patient a reward without reckoning, meaning an unlimited reward. That is only because of the virtue of patience and its high status before Allah, and indicates that Allah is the source of help in all situations.
End quote from Tafseer as-Sa‘di (p. 721).
And Allah knows best.