Answered by Shaykh Rami Nsour
Question: What is the Maliki school’s position on combining prayers due to rain or bad weather in general, and what are the conditions to make it valid? We live in Florida and it rains here frequently in the summer. Also, even though some masajid are far, we travel in cars so there is not much of a hassle when it comes to getting wet or dirty from the rain and puddles.
The Ruling of Joining Prayers due to Rain
According to the Maliki madhab, it is a recommended dispensation (rukhsa mandubah) to join Maghrib and Isha at Maghrib time on the night when it is raining. Maghrib would not be delayed until Isha but rather you bring Isha forward and pray it after Maghrib. Joining of Dhuhr and Asr due to rain is not allowed according to the Maliki school.
The conditions for this dispensation is that this only be done due to rain, hail or heavy snow. The joining can also be done if there is both darkness (due to heavy cloud cover) and muddy pathways, but not if there is only one or the other. This joining would be done in what is considered a masjid but not another place like a musallah or a school.
The Method of Joining
The call to prayer (adhan) would be given for Maghrib right after complete sundown and done on the minaret as usual. Then Maghrib prayer is delayed a short while and followed immediately by Isha prayer. The only thing that would be done between Maghrib and Isha would be a call to prayer (adhan) for Isha but done inside the masjid with a lower voice followed an iqamah. No extra prayers (nafila) should be done between Maghrib and Isha.
[Dusuqi, Hashiya al-Sharh al Kabir]
source : http://seekersguidance.org/ans-blog/2013/06/19/joining-prayers-due-to-rain-in-the-maliki-school/