Liaison office of Grand Ayatullah Sayyid Ali Al Sistani (L.M.H.L) in London, Europe, North and South America.
Prayer Performed Behind a Non-Believer
10. What is the ruling on prayer performed behind a non-believer (ghayeril mumin), especially if he holds it before its prescribed time?
"[The prayer] is not in order, unless its prescribed time was already on". Al-Manasik, p366.