The Ruling on combining the Two Evening Prayers during Rain and for Business
Question :
Is it permissible to combine the Maghrib and Isha' prayers on rainy nights, when there is a lot of mud on the road to the mosque? And is it permissible for the businessman to combine them, bring the Isha' prayer forward to Maghrib time, in order for his shop to remain open after it?
Answer:
It is permissible to combine the two night prayers due to rain, if it is heavy and continuous, or if the roads are full of mud and mire and slipperiness and the way is unlit and the cold is severe. As for the merchants combining their prayers in order to keep their shops open all the time, it is not permissible; instead, they must be closed during prayers.
Source:
Ibn Jibreen
Fatawa Islamiyah, Vol. 2 Pages 224-225