The Ruling on Breaking off the Prayer for Some Necessity
Question :
I was praying the Dhuha prayer in my house, and after I had made the opening Takbir and recited Al- Fatihah, someone knocked on the door, so I made the Taslim and opened the door. Then I returned and prayed again, making the Takbir from the beginning. Should I make any expiation for it?
Answer:
There is no objection to breaking off the prayer - even if it were an obligatory prayer for some necessity, such as you have mentioned. Because the person knocking on the door may raise his voice or knock louder or even bang on the door, which will cause annoyance and prevent one from performing prayer in the required manner. As for breaking off the prayer without necessity, it is not permissible, but if a person did so and then repeated the prayer, then there is no sin upon him - Allah willing and there is no expiation required, except to regret it and turn in repentance (to Allah).
Source:
Ibn Jibreen
Fatawa Islamiyah, Vol. 2 Pages 246-247