1 in 5 Brits Don't Know Jesus's Birth Marked on Christmas Day
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 Harts 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,