I don't remember what season the story was set in (I believe 5 or 6 at least), but there was this one part of the story where Buffy, Spike, and I think Xander are hunting down some demon or warlock or something, because he had kidnapped a baby and was going to use the child for a ritual. They managed to mess up the first attempt, but they lost track of the demon (or warlock), and Spike made a comment about if the baby was baptized or not, Xander begins to make a snide remark, but Buffy quickly shuts him up and asks Spike to explain. Spike says something about religion playing a big part in rituals, and that if the child was untouched the ritual would have been more potent or something, I don't really remember much about it.

EDIT: Sorry, this was meant to be in Find-A-Fic. I was, and still am, rather sleep deprived when I typed this in this section. I didn't notice this was Fic Recs. Could a mod either move this or take it down from here? Sorry for the inconvenience.