Questions having to do with cutting the hair or shaving it off
Question

                1. Is there any hadith which states that the Prophet (blessings and peace of Allah be upon him) prayed for the barber?
2. Is there any hadith which states that the Prophet told men to keep their hair long, coming down to the shoulders?
3. Can you tell me the hadith in which the Prophet (blessings and peace of Allah be upon him) said: “Let the beard grow and shave the moustache”?
4. Can you give me a reference in which it says that Abu Bakr went to the barber and paid double the fee?
5. Is there any hadith which says that there are certain days on which it is not allowed to cut the hair?
Praise be to Allah.Firstly:
We have not come across any hadith in which it says that the Prophet (blessings and peace of Allah be upon him) offered any specific du‘aa’ (supplication) for the barber.
But if the barber’s work was done by way of kindness and doing a favour, and he did not take any payment for that, then his favour should be returned by praying for him.
It was narrated that ‘Abdullah ibn ‘Umar said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “If anyone does you a favour, then reciprocate, and if you do not have any means of reciprocating, then pray for him until you think that you have reciprocated (by praying for him).”
Narrated by Abu Dawood (1672) and an-Nasaa’i (2567). Shaykh al-Albaani (may Allah have mercy on him) said: al-Haakim said: It is saheeh according to the conditions of al-Bukhaari and Muslim, and adh-Dhahabi agreed with him, and it is as they both said. End quote from as-Silsilah as-Saheehah (1/510).
Secondly:
With regard to a man letting his hair grow down to his shoulders, there is no report to suggest that the Prophet (blessings and peace of Allah be upon him) instructed them to do that or encouraged them to do it. Rather it is narrated that the Prophet (blessings and peace of Allah be upon him) did that.
It was narrated from Anas (blessings and peace of Allah be upon him) that the hair of the Messenger of Allah (blessings and peace of Allah be upon him) came down to his shoulders.
Narrated by al-Bukhaari (5903) and Muslim (2338).
Sometimes it was shorter than that, and sometimes it was a little longer than that, as was the custom of the Arabs at the time of the Prophet (blessings and peace of Allah be upon him).
Letting the hair grow long in and of itself does not come under the heading of Sunnahs that we are encouraged to follow. Rather it comes under the heading of custom and tradition. This has been discussed previously in the answer to question no. 69822.
Thirdly:
The command to let the beard grow and trim the moustache has been narrated in reports, such as the hadith of Ibn ‘Umar, according to which the Prophet (blessings and peace of Allah be upon him) said: “Trim your moustaches and let your beards grow.” Narrated by al-Bukhaari (5893) and Muslim (259).
Imam Muslim (260) narrated that Abu Hurayrah said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “Trim the moustache and let the beard grow: be different from the Magians.”
For more information, please see the answers to questions no. 1189 and 75525.
Fourthly:
We have not come across any report to suggest that Abu Bakr (may Allah be pleased with him) paid the barber double his fee.
Fifthly:
It was narrated that it is not allowed to cut one’s hair on two occasions:

For the pilgrim who is performing Hajj or ‘umrah, whilst performing Hajj or ‘umrah.

Allah, may He be exalted, says (interpretation of the meaning):
“And complete the hajj and 'umrah for Allah. But if you are prevented, then [offer] what can be obtained with ease of sacrificial animals. And do not shave your heads until the sacrificial animal has reached its place of slaughter”
[al-Baqarah 2:196].
Ibn ‘Abd al-Barr (may Allah have mercy on him) said:
The scholars are unanimously agreed that it is obligatory for the muhrim (pilgrim in the state of ihram) to refrain from removing any hair from his head from the moment he enters ihram for Hajj until he stones Jamrat al-‘Aqabah at the appointed time. End quote from at-Tamheed (7/266).

From the night when the month of Dhu’l-Hijjah begins, until the udhiyah (sacrifice) is offered.

This applies only to the one who intends to offer the sacrifice. This has been discussed in detail in the answers to questions no. 83381 and 70290.
At all times other than these, there is nothing wrong with cutting one’s hair.
And Allah knows best.