For a quick reference I would recommend Rambam's Mishneh Torah, Hil.
Teshuvah ch.8 and the commentaries there (particularly Kesef Mishna and
Haghos Maimonios). For a much more extensive discussion see the final shaar
[chapter] of the Ramban's Toras Adam called "Shaar HaGmul"(which is also
cited in the standard prints of the Rambam).
Eliezer C. Abrahamson
176 East 9th St., Lakewood, NJ 08701
(908) 905-6877 e-mail: Abrahamson@juno.com