What is the ruling on fighting a Muslim brother in the Masjid?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Mosques should be free from fighting, noise, shouting and loud talking, buying and selling, or even enquiring about a lost property as all this is contrary to their merit and status.

Allah Says (interpretation of meaning): {In houses (mosques), which Allâh has ordered to be raised (to be cleaned, and to be honoured), in them His Name is glorified in the mornings and in the afternoons or the evenings, Men whom neither trade nor sale diverts them from the Remembrance of Allâh (with heart and tongue), nor from performing As­Salât (Iqâmat-as-Salât), nor from giving the Zakât. They fear a Day when hearts and eyes will be overturned (from the horror of the torment of the Day of Resurrection).}[24:36-37].

Muslim reported that the Prophet (Sallallahu Alaihi wa Sallam) said to the Bedouin Arab who urinated in the mosque: "These mosques are not befitting this urine or any impurity.  They are built for the remembrance of Allah, the prayer and recitation of the Qur'an."

Al Nawawi said in his explanation of this Hadith: ‘It is about the maintenance of the mosques and their purification from impurities, spitting, raising one’s voice, fighting, selling and buying, and all other kinds of contracts.’

If someone has committed one of the above, he should be advised and reminded of the above texts.

Allah knows best.