Question:
If someone is praying and there is an urgent need such as maintenance work, someone knocking on the door, or a child crying loudly, and the person stops the prayer to respond, is there any expiation required for breaking the prayer?
Answer:
The answer is that breaking the prayer is allowed when there is a valid necessity. Islam does not teach that once someone begins prayer he must ignore everything happening around him. If a child is crying, the person praying does not know what caused it—perhaps the child is in danger or pain.
In such a case the prayer may be stopped to attend to the situation. There are even narrations encouraging killing harmful creatures even while praying, which shows that dealing with urgent matters takes priority.
However, when the prayer is broken it cannot be continued from the point where it stopped. Once the issue is resolved, the person must start the prayer again from the beginning. There is no expiation required because the person did not commit a sin; he acted according to what Islam permits.