Majmu' al-Fatawa - Ibn Taimiya - (31/209)

He answered—may Allah have mercy on him:

Praise be to Allah. Yes, if this benefits the mosque and its congregation, and the only concern is that ablution would be performed inside the mosque, then it is permissible to do so. Performing ablution in a mosque is permissible; indeed, the majority of scholars do not even regard it as disliked. And Allah knows best.

He was asked:

An old, closed mosque collapsed and was demolished, then rebuilt to its former length and width. The builder raised it above its former level and extended it forward. There had been a private chamber beneath it, and he built a dwelling underneath for the benefit of the mosque. Is it permissible to renovate the dwelling and live in it?

He answered:

Praise be to Allah. Yes, any work that benefits the mosque and its congregation may be carried out, including renovating the building, altering its layout, and similar work. And Allah, Glorified is He, knows best.

فَأَجَابَ - رَحِمَهُ اللَّهُ -: الْحَمْدُ لِلَّهِ، نَعَمْ إذَا كَانَ هَذَا مَصْلَحَةً لِلْمَسْجِدِ وَأَهْلِهِ وَلَيْسَ فِيهِ مَحْذُورٌ إلَّا مُجَرَّدُ الْوُضُوءِ فِي الْمَسْجِدِ جَازَ أَنْ يُفْعَلَ ذَلِكَ؛ فَإِنَّ الْوُضُوءَ فِي الْمَسْجِدِ جَائِزٌ؛ بَلْ لَا يُكْرَهُ عِنْدَ جُمْهُورِ الْعُلَمَاءِ. وَاَللَّهُ أَعْلَمُ. وَسُئِلَ: عَنْ مَسْجِدٍ مُغْلَقٍ عَتِيقٍ فَسَقَطَ وَهُدِمَ وَأُعِيدَ مِثْلَ مَا كَانَ فِي طُولِهِ وَعَرْضِهِ وَرَفْعِهِ الْبَانِي لَهُ عَنْ مَا كَانَ عَلَيْهِ وَقَدَّمَهُ إلَى قُدَّامُ وَكَانَ تَحْتَهُ خَلْوَةٌ فَعَمِلَ تَحْتَهُ بَيْتًا لِمَصْلَحَةِ الْمَسْجِدِ. فَهَلْ يَجُوزُ تَجْدِيدُ الْبَيْتِ وَسَكَنِهِ؟ فَأَجَابَ: الْحَمْدُ لِلَّهِ، نَعَمْ يَجُوز أَنْ يَعْمَلَ فِي ذَلِكَ مَا كَانَ مَصْلَحَةً لِلْمَسْجِدِ وَأَهْلِهِ: مِنْ تَجْدِيدِ عِمَارَةٍ وَتَغْيِيرِ الْعِمَارَةِ مِنْ صُورَةٍ إلَى صُورَةٍ وَنَحْوِ ذَلِكَ وَاَللَّهُ سُبْحَانَهُ أَعْلَمُ.