Fiqh-us-Sunnah Volume 2, Supererogatory Prayer, Fiqh 2.079A.

The salah is not invalidated by anything (passing in front of the praying person).

‘Ali, ‘Uthman, ibn al-Musayyab, ash-Sh’abiy, Malik, ash-Shaf’i, Sufyan al-Thauri and the Hanafi scholars are of the opinion that the salah is not invalidated by anything which passes in front of a person. This is based on the hadith recorded by Abu Dawud from Abu al-Waddak who says: “A young person tried to pass in front of Abu Sa’id while he was praying. Abu Sa’id held him off and then the young man tried again. Abu Sa’id pushed him off. This happened three times and when [Abu Sa’id] finished [the prayer], he said: ‘The salah is not invalidated by anything but the Messenger of Allah said: ‘Repulse [the person who is trying to pass in front of you] to the best of your ability for he is a devil.'”