Praise be to Allah.
There is a concession allowing Maghrib and ‘Isha’ prayers to be joined at the time of Maghrib, with one adhaan and iqaamah for each of them, when there is rain that soaks people’s clothes, when going back to the mosque for ‘Isha’ will cause hardship. This is according to the more correct of the two scholarly opinions.
Similarly it is permissible to join them when it is very muddy, according to the correct scholarly view, so as to avoid hardship and difficulty. Allah says (interpretation of the meaning):
“and has not laid upon you in religion any hardship” [al-Hajj 22:78]
“Allah burdens not a person beyond his scope” [al-Baqarah 2:286]
Abaan ibn ‘Uthmaan (may Allah be pleased with him) joined Maghrib and ‘Isha’ on rainy nights, when there was a group of senior scholars from among the Taabi’een, and it is not known that any of them objected, so that meant there was consensus.
That was mentioned by Ibn Qudamah in al-Mughni. It is also allowed for a person who is very sick to join Zuhr and ‘Asr at the time of either of them, depending on what is easier for him, and he can join Maghrib and ‘Isha’ likewise, so as to avoid hardship.
Fatawa al-Lajnah al-Daa’imah li’l-Buhoot al-‘Ilmiyyah wa’l-Ifta’, 8/135.
If it is asked: can we join prayers because of rain in the mosque or at home? The answer is:
What is prescribed is for the people who pray in the mosque to join their prayers if there is a reason that justifies joining them, such as rain, so as to attain the reward of praying in congregation whilst also being kind to the people. This is what it says in the saheeh ahadith.
With regard to joining the prayers at home for the reason mentioned, that is not permissible because it is not narrated in sharee’ah and there is no excuse that would permit joining the prayers.
Fatawa al-Lajnah al-Daa’imah li’l-Buhooth al-‘Ilmiyyah wa’l-Ifta’, 8/134.