From the gemara on daf 37 it would appear that it is ok to get paid for a mitzvah - the only problem is if it is on Shabbos. However from daf 39 (re bikur cholim) it seems that it's not ok. Unless we say that on daf 37 for eg guarding the poroh there is schar batolo but it doesn't state that. Any ideas?
A Lerner, London, UK
Even by Bikur Cholim, if one does more than the minimum required (i.e. "Yeshivah") then he may get paid. However, I think that the Isur to take money only applies to Mitzvos of Gemilus Chasadim and Talmud Torah, about which it is said, "Mah Hu b'Chinam Af Atah b'Chinam."
D. Zupnik