Quran 18:26 — The Cave (Al-Kahf)

Say, "GOD is the best knower of how long they stayed there." He knows all secrets in the heavens and the earth. By His grace you can see; by His grace you can hear. There is none beside Him as Lord and Master, and He never permits any partners to share in His kingship.

[18:25] They stayed in their cave three hundred years, increased by nine.*

[18:27] You shall recite what is revealed to you of your Lord's scripture. Nothing shall abrogate His words, and you shall not find any other source beside it.