Firstly: 

The scholars differed concerning the ruling on men wearing underwear that covers the most private part of the ‘awrah. Some of them are of the view that it is permissible even in cases other than those of necessity. They said: There is no text that forbids it among the things that the muhrim (pilgrim in ihraam) is not allowed to wear. 

But the majority are of the view that wearing it is not permissible by analogy with trousers. Some scholars were of the view that it is even more forbidden than trousers. 

Shaykh al-Islam Ibn Taymiyah (may Allaah have mercy on him) said: 

Similarly, underwear is more (forbidden) than trousers. End quote. 

Majmoo’al-Fataawa (21/206). 

Ibn al-Qayyim (may Allaah have mercy on him) said: 

Al-Muzni said: The fuqaha’ from the time of the Messenger of Allaah (peace and blessings of Allaah be upon him) until now use analogy to derive rulings on matters of religion.  

He said:  

They are unanimously agreed that what appears to be valid on the basis of analogy is valid, and what appears to be invalid on the basis of analogy is invalid, and it is not permissible for anyone to reject analogy, because it is comparing between matters and seeking the similarities between them. 

For example, the Prophet (peace and blessings of Allaah be upon him) forbade the pilgrim in ihraam to wear a shirt, trousers, head covering and khufoof, and he did not restrict it to these things only, rather the prohibition also applies to cloaks, caps, kufis (white cotton skullcaps), socks and underwear, etc. End quote. 

I’laam al-Muwaqqi’een (1/205-207). 

Thus it is clear that those who regard it as permissible to wear underwear on the basis that it is not mentioned in the hadeeth in which the Prophet (peace and blessings of Allaah be upon him) described what the pilgrim in ihraam should not wear, are mistaken. 

Ibn ‘Abd al-Barr (may Allaah have mercy on him) said: 

Under the same heading as the clothes mentioned in this hadeeth, such as shirts, trousers, burnouses etc, come all kinds of tailored clothes, so it is not permissible for the pilgrim in ihraam to wear any of them, according to all of the scholars. 

Al-Tamheed (15/104). 

Al-Haafiz Ibn Hajar (may Allaah have mercy on him) said: ‘Iyaad said: The Muslims are unanimously agreed that the things mentioned in this hadeeth cannot be worn by the muhrim, and that the reference to shirts and pants includes all tailored items, and burnouses and turbans include all things that cover the head, whether they are tailored or otherwise, and khufoof refers to everything that covers the foot. End quote. 

What is meant by tailored clothes is that which is worn on the place for which it is made, even if it is part of the body. End quote. 

Fath al-Baari (3/402) 

Those who say that it is permissible for the muhrim to wear underwear quoted as evidence the report from ‘Aa’ishah (may Allaah be pleased with her) which said that she allowed porters to wear it, and the report that ‘Ammaar ibn Yaasir used to wear it. 

1 –The report of ‘Aa’ishah 

al-Bukhaari (may Allaah have mercy on him) said in his Saheeh (2/558): 

Chapter on putting on perfume at the time of entering ihraam and what is worn when wanting to enter ihraam. ‘Aa’ishah (may Allaah be pleased with her) did not see anything wrong with wearing underwear for those who were lifting up her howdah (onto the camel). 

End quote. 

Al-Haafiz Ibn Hajar (may Allaah have mercy on him) said: 

The report of ‘Aa’ishah reached Sa’eed ibn Mansoor via ‘Abd al-Rahmaan ibn al-Qaasim from his father from ‘Aa’ishah, that she did Hajj with two slaves of hers and when they lifted up (the howdah) something of them would appear, so she told them to put on underwear, and they put it on when they were in ihraam. 

This is a refutation of Ibn al-Teen in his saying that ‘Aa’ishah was referring to women, because they are allowed to wear tailored clothes (in ihraam), unlike men. It is as if this was the view held by ‘Aa’ishah, otherwise the majority are of the view that there is no difference between underwear and trousers with regard to it being forbidden for the pilgrim in ihraam. End quote from Fath al-Baari (3/397). 

The answer to this is that ‘Aa’ishah told them to do that as a case of necessity, because their ‘awrah was becoming uncovered; it does not indicate that it is permissible in cases other than necessity. 

2 –The report of ‘Ammaar 

Ibn Abi Shaybah narrated that Habeeb ibn Abi Thaabit said:  I saw ‘Ammaar ibn Yaasir wearing an undergarment when he was in ‘Arafaat.

Musannaf Ibn Abi Shaybah (6/34). 

This may be understood as being a case of necessity, as there is a report narrated by Ibn Shabbah in Akhbaar al-Madeenah (3/1100) which indicates that ‘Ammaar ibn Yaasir (may Allaah be pleased with him) was injured at the time of ‘Uthmaan ibn ‘Affaan (may Allaah be pleased with him), concerning which he said: “I cannot control my urine.” 

In al-Nihaayah fi Ghareeb al-Athar (2/126) it says: 

In the hadeeth of ‘Abd Khayr it says: I saw ‘Ammaar wearing an undergarment, and he said: “I have a bladder problem.”  

The undergarment is short pants that cover the private parts only. 

These reports, even though they are ahaad reports, still indicate that there is a basis for that. 

The correct view is that the man who is in ihraam is not allowed to wear an undergarment, and the report narrated from ‘Aa’ishah may be understood as referring to a case of necessity; it does not suggest that the one who wears it does not have to offer a fidyah (ransom). 

The report from ‘Ammaar ibn Yaasir may also be understood as referring to a case of necessity, as he was suffering from a bladder problem. 

Shaykh Muhammad al-Ameen al-Shanqeeti (may Allaah have mercy on him) said:  

From the report of ‘Aa’ishah it seems that she granted a concession allowing those who were lifting up her hawdah to wear undergarments due to necessity, as their ‘awrahs were becoming uncovered. This indicates that it is not permissible except in cases of necessity. And Allaah knows best. End quote. 

Adwa’ al-Bayaan (5/464) 

Secondly: 

It is permissible for one who is working as a porter – for example – and is afraid that his ‘awrah may become uncovered, to wear an undergarment. It is also permissible for one whose skin is broken due to chafing, and he fears that he may be harmed. It is also permissible for one who has a wound in the ‘awrah area and needs to cover it, and for one who is suffering from incontinence – which is akin to the case of ‘Ammaar ibn Yaasir. In all of these and similar cases, the one who wears it has to offer a fidyah, which is feeding six poor persons, or fasting for three days, or slaughtering a sheep. 

Allaah says (interpretation of the meaning): 

“And whosoever of you is ill or has an ailment in his scalp (necessitating shaving), he must pay a Fidyah (ransom) of either observing Sawm (fasts) (three days) or giving Sadaqah (charity — feeding six poor persons) or offering sacrifice (one sheep)”

[al-Baqarah 2:196]

It was narrated that ‘Abd-Allaah ibn Ma’qil said: I sat with Ka’b ibn ‘Ujrah (may Allaah be pleased with him) and asked him about the fidyah. He said: That was revealed concerning me in particular but it applies to all of you. I was brought to the Messenger of Allaah (peace and blessings of Allaah be upon him) with lice crawling on my face. He said: “I did not think that your problem had become as bad as I see it. Can you afford a sheep?” I said: No. He said: “Then fast for three days, or feed six poor persons, giving each one half a saa’.” 

Narrated by al-Bukhaari (1721)and Muslim (1201). 

Shaykh Muhammad ibn Saalih al-‘Uthaymeen was asked about a pilgrim in ihraam wearing an undergarment, because if he does not wear it he will suffer some harm. 

He replied: 

If he is afraid that he may suffer some harm, there is nothing wrong with him wearing it, but if he can feed six poor persons, giving each one half a saa’, that is better. 

Liqaa’aat al-Baab il-Maftooh (177/question no. 16). 

See also the answers to questions no. 20870 and 49033. 

And Allaah knows best.