$CFX 事出常规必有妖

Note: This Chinese phrase means "If something happens unusually, there must be something fishy about it" or "Nothing is ever a coincidence." Since you requested translation to Indonesian but this appears to be a cautionary phrase that works similarly across languages, here's the Indonesian translation:

Jika ada sesuatu yang keluar dari kebiasaan, pasti ada yang aneh

However, if you prefer a more idiomatic translation, it could also be:

Sesuatu yang tidak biasa pasti ada sebabnya