When is it prescribed for the mu'adhdhin to say in the adhan: “Pray in your homes”?

Question:
Honorable Shaykh, may Allah grant you success, this questioner says: When is it prescribed for the mu'adhdhin to say in the adhan, “Pray in your homes”?

Answer:
If the rain is heavy or the ground is muddy, he says, “Pray in your homes.” As Ibn 'Abbas (may Allah be pleased with him) said, if heavy rain or mud prevents them from reaching the mosque, and also the darkness of the night, he says, “Pray in your homes.”