PHP was written in C. To quote Rasmus Lerdorf:

“I wonder why people keep writing that PHP was ever written in Perl. It never was. #php”

The PHP history page at one point claimed it was:

https://web.archive.org/web/20090426061624/http://us3.php.ne...

He may have had some Perl scripts on his computer before the 1.0 C release, but that’s a far cry from “PHP was written in Perl”.

Thanks for debunking, I'll stop spreading lies now ^^;