Abu Hurairah (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings of Allah be upon him) said: "When you see a person buying or selling in the mosque, say: May Allah not grant profit in your trade. And when you see a person searching for a lost item in the mosque (announcing it), say: May Allah not return your item to you." __REF_N__ Imam Tirmidhi says:
1- The hadith of Abu Hurairah (may Allah be pleased with him) is Hasan Gharib,
2- Some people of knowledge act upon this, they consider buying and selling in the mosque to be impermissible. This is also the opinion of Ahmad and Ishaq bin Rahwayh,
3- Some people of knowledge have permitted buying and selling in this matter. __XREF_N__

´'Uthman bin Abi Al-'As narrated:` "The Messenger of Allah (S.A.W) came to me while I had a pain that almost ruined me. So,the Messenger of Allah (S.A.W) said: 'Rub it with your right hand seven times and say A`udhu bi `Izzatillah Wa Qudratihi wa Sultanihi min sharri ma ajid." ("I seek refuge in Allah's might, power, an authority, from the evil of what I suffer.)" He said: "So I did it, and Allah removed what I had, and I never ceased telling my family and others to do it."