Is it obligatory to kill a snake or a serpent during prayer, and how is that done without invalidating or redoing the prayer? And what is the ruling on killing snakes outside of prayer, and how does one seek permission from house snakes?

It is permissible for a worshiper to kill a snake or a scorpion during prayer, based on the hadith: "Kill the two black ones during prayer: the snake and the scorpion." If this results in excessive movement, it invalidates the prayer according to many scholars, and the estimation of excessive movement is left to common practice. Some scholars dislike killing them during prayer if they are not moving towards the worshiper. Some scholars hold that continuous excessive movement invalidates the prayer, while minor movement does not.

The act of killing snakes is generally recommended, not obligatory, except for the snakes of the Prophet's city (Medina), which should be warned before being killed. Their warning should be for three days, or three times.