Short answer
A large bun or volumiser worn high under the hijab to make the head look bigger falls under the Prophet's ﷺ warning about women whose heads look like camels' humps, so it should be avoided. Tying long hair in a low, flat bun simply to keep it tidy is fine.
Building up the head under the scarf so that it rises like a hump, for show, is not allowed because of the hadith in Sahih Muslim. Gathering the hair in a simple low bun for practicality is permissible.
The four schools agree on this.
Explanation
In a hadith in Sahih Muslim the Prophet ﷺ described two kinds of the people of the Fire he had not yet seen. One was women who are clothed yet naked, who sway and make others sway, with heads like the leaning humps of Bactrian camels. Bactrian camels have large humps, and the image is of a head made to look tall and swollen.
Imam Nawawi explained it as women who wind cloth or other material on their heads to make them look bigger. Many contemporary scholars apply this directly to the oversized bun and the volumising clips sold for wearing under a hijab, which raise a mound at the back or top of the head.
Practical guidance:
- Avoid: a high bun or volumising scrunchie whose purpose is to give the hijab height and shape.
- Fine: tying long hair into a low bun or plait at the nape so the scarf sits neatly.
- Fine: an underscarf or cap to hold the hijab in place.
- The test: is it there to keep the hair tidy, or to make the head stand out?
The wider lesson of the hadith is that hijab is meant to cover beauty, not to repackage it. See the conditions of a correct hijab and the hijab guide.
The evidence
Quran, Surah An-Noor 24:31
وَقُل لِّلْمُؤْمِنَٰتِ يَغْضُضْنَ مِنْ أَبْصَٰرِهِنَّ وَيَحْفَظْنَ فُرُوجَهُنَّ وَلَا يُبْدِينَ زِينَتَهُنَّ إِلَّا مَا ظَهَرَ مِنْهَا ۖ وَلْيَضْرِبْنَ بِخُمُرِهِنَّ عَلَىٰ جُيُوبِهِنَّ ۖ وَلَا يُبْدِينَ زِينَتَهُنَّ إِلَّا لِبُعُولَتِهِنَّ أَوْ ءَابَآئِهِنَّ أَوْ ءَابَآءِ بُعُولَتِهِنَّ أَوْ أَبْنَآئِهِنَّ أَوْ أَبْنَآءِ بُعُولَتِهِنَّ أَوْ إِخْوَٰنِهِنَّ أَوْ بَنِىٓ إِخْوَٰنِهِنَّ أَوْ بَنِىٓ أَخَوَٰتِهِنَّ أَوْ نِسَآئِهِنَّ أَوْ مَا مَلَكَتْ أَيْمَٰنُهُنَّ أَوِ ٱلتَّٰبِعِينَ غَيْرِ أُو۟لِى ٱلْإِرْبَةِ مِنَ ٱلرِّجَالِ أَوِ ٱلطِّفْلِ ٱلَّذِينَ لَمْ يَظْهَرُوا۟ عَلَىٰ عَوْرَٰتِ ٱلنِّسَآءِ ۖ وَلَا يَضْرِبْنَ بِأَرْجُلِهِنَّ لِيُعْلَمَ مَا يُخْفِينَ مِن زِينَتِهِنَّ ۚ وَتُوبُوٓا۟ إِلَى ٱللَّهِ جَمِيعًا أَيُّهَ ٱلْمُؤْمِنُونَ لَعَلَّكُمْ تُفْلِحُونَ ﴿٣١﴾
And tell the believing women to reduce [some] of their vision and guard their private parts and not expose their adornment except that which [necessarily] appears thereof and to wrap [a portion of] their headcovers over their chests and not expose their adornment except to their husbands, their fathers, their husbands' fathers, their sons, their husbands' sons, their brothers, their brothers' sons, their sisters' sons, their women, that which their right hands possess, or those male attendants having no physical desire, or children who are not yet aware of the private aspects of women. And let them not stamp their feet to make known what they conceal of their adornment. And turn to Allah in repentance, all of you, O believers, that you might succeed.
Adornment is kept from non-mahram men.
Quran, Surah Al-Ahzaab 33:33
وَقَرْنَ فِى بُيُوتِكُنَّ وَلَا تَبَرَّجْنَ تَبَرُّجَ ٱلْجَٰهِلِيَّةِ ٱلْأُولَىٰ ۖ وَأَقِمْنَ ٱلصَّلَوٰةَ وَءَاتِينَ ٱلزَّكَوٰةَ وَأَطِعْنَ ٱللَّهَ وَرَسُولَهُۥٓ ۚ إِنَّمَا يُرِيدُ ٱللَّهُ لِيُذْهِبَ عَنكُمُ ٱلرِّجْسَ أَهْلَ ٱلْبَيْتِ وَيُطَهِّرَكُمْ تَطْهِيرًۭا ﴿٣٣﴾
And abide in your houses and do not display yourselves as [was] the display of the former times of ignorance. And establish prayer and give zakah and obey Allah and His Messenger. Allah intends only to remove from you the impurity [of sin], O people of the [Prophet's] household, and to purify you with [extensive] purification.
Forbids making a display of oneself.
Sahih Muslim 2128
Sahih... رءوسهن كأسنمة البخت المائلة ...
"Their heads are like the leaning humps of Bactrian camels."
Making the head look large and striking under the covering is condemned.
Where the ruling is recorded
- Sharh Sahih Muslim (Nawawi), Kitab al-Libas wa al-Zinah, the hadith of women clothed yet naked. Explains the camel-hump heads as women who enlarge their heads by winding cloth on them.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.