My mother lives next to a congregational mosque. Between her and the mosque is a small street. She hear the adhan and the prayer and she continues to follow the Imam in her prayer in her house. Is that allowable for her? If it is not allowed, what should she do about the prayers that she performed in that manner over the years. I hope you can benefit us in this matter, may Allah reward you.
If the situation is as you mentioned in the question, she cannot follow the Imam of the mosque in her prayer unless she sees the Imam or some of the rows of the followers. If she does not see any of them, then the strongest opinion among the statements of the scholars is that she does not follow the Imam in the prayer. As for what has passed of her prayers, she does not have to repeat them, Allah willing, because there is no clear evidence that they are invalid prayers. This question is an area of ijtehad [juristic reasoning] by the scholars. The safest and strongest opinion is as we have mentioned.
Shaikh ibn Baz