Question Summary:
Using interest for construction of toilets for the Masjid

Question Detail:

Can I use money generated from bank interest for the construction of toilet in Masjid?

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
Interest money is unlawful and filthy. Interest money should be disposed of to the poor and needy.[1]
It is impermissible to use the interest money in constructing toilets for the Masjid. The Masjid is the house of Allah. Only pure and Halal money should be used for the construction of the Masjid and anything associated with the Masjid.[2]
Consider the following Hadith:
عنْ أَبِي هُرَيْرَةَ - رضي الله عنه - قَالَ قَالَ رَسُولُ اللهِ - صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ - أَيُّهَا النَّاسُ إِنَّ اللهَ طَيِّبٌ لَا يَقْبَلُ إِلَّا طَيِّبًا
Abu Huraira (Radhiyallahu Anhu) narrates that Rasulullah (ﷺ) said: O’ people, verily Allah is pure and accepts only that which is pure.[3]
 
And Allah Ta’āla Knows Best
Abdullah ibn Mohammed Aijaz
Student Darul Iftaa
Baltimore, USA 
Checked and Approved by,
Mufti Ebrahim Desai.