Abu Hurayrah رضي الله عنه said:

Allaah's Messenger صلى الله عليه وسلم said:

"When anyone of you wakes up, he should rinse his nose three times. Verily Shaytan spends the night upon his nostrils."

In another narration he صلى الله عليه وسلم said:

''When one of you performs wudu, let him snuff water water in his nose and then blow it out.''


{ Imam Al Bukhari #3121, Muslim #23 fe Sahihain }

Blowing the nose is an obligation in the Hanbali school of fiqh, and a sunnah with the majority of scholars.

Imam Muhammad Salih ibn Uthaymeen رحمه الله commented:

"This hadeeth proves that Shaytan has the ability to do things and we don't have the ability to perceive it. Shaytan spends the night in our nose and we don't know how. We can't make out how anyone could shape their body for the size of a nostril. However if it was something that crawled the size of an atom we could see how.
Nonetheless the world of the Shayaateen and Jinn is hidden from us. And likewise the world of the Angels is hidden from us. There is an Angel on our right and left side that accompany us. Do we feel them? We don't feel them, but we believe this to be a fact.
The hadeeth proves that Allaah has given Shaytan the ability to overpower us. Therefore he صلى الله عليه وسلم informed us about this act of Shaytan, so we could be aware of his evil and realise our need for Allaah."

{ Sharh Saheeh Muslim }

Imam Muhammad Abdur Rauf Al Munaawi رحمه الله commented:

"Shaytaan also chooses the nose because the eyes are for looking and pondering over the creations in the heavens and earth. The mouth is for remembering Allaah. The ears are for listening to knowledge and Allaah's remembrances. However the nose doesn't have any of these traits. Therefore this is an entrance for Shaytan into man's body to whisper to him.

{ Faydul Qadeer Sharh jami as Saghir #436 }

*** Allaah عزوجل knows best ***