Classical, biblical, and similar names ending in a sibilant, especially if they are polysyllabic, do not take an added s in the possessive; among sources giving exceptions of this kind are The Times and The Elements of Style, which make general stipulations, and Vanderbilt University, which mentions only Moses and Jesus. As a particular case, Jesus' [my emphasis] is very commonly written instead of Jesus's – even by people who would otherwise add 's in, for example, James's or Chris's. Jesus' is referred to as "an accepted liturgical archaism" in Hart’s Rules.
- Wikipedia
Please don't groan because I cite Wikipedia - it's electronic, and easier to access for this post. But it says essentially the same thing as my Bible (I'm a Technical Editor), The Chicago Manual of Style.
Regards,
Thanks for the clarification.