What Happens when a Muqtadi's Vomit Messes the Imaam's Clothing?

Q: Taharaat-31: A Muqtadi in yesterday's Maghrib salaah who was Standing direct behind the Imaam happened to vomit a mouthful so forcefully that the Imaam's Kurta, legs and Musalla were all messed with the vomit while he was leading the salaah. There amount of the vomit was clearly more than the size of a Dirham. Does the salaah have to be repeated?

Answer: Vomit that is more than a mouthful is regarded to be Najaasat Ghaleezah (a severe form of impurity) and although an amount less than a Dirham will be pardoned, if it is more, the salaah will be invalid. It must therefore be repeated. The extent of a Dirham is that of a palm, which can be ascertained by filling the palm with water, opening the palm and then seeing how much water is left. This will be the forgiven amount.

Fatawa Rahimiyyah vol.2