Where did Friday the 13th come from?

If Friday was the thirteenth, Saturday would be the fourteenth, and Sunday would be the fifteenth according to a Gentile calendar.

If you are from Israel, the thirteenth starts on Thursday the night prior and ends at sundown on Friday. The fourteenth starts on Friday at sundown and ends Saturday at sundown.

If Israel was told to sacrifice the Passover lamb on the fourteenth at twilight, and this was the week, it would have been done on Friday night, not Saturday.

The night the angel of death killed all the firstborn of Egypt I believe was on Friday the 13th, which was the 14th of Nisan that year.