Natural law is “written on our hearts” according to the Bible:
“They show that the work of the law is written on their hearts, while their conscience also bears witness, and their conflicting thoughts accuse or even excuse them.”
Romans 2:15, English Standard Version
“For this is the covenant that I will make with the house of Israel after those days, declares the LORD: I will put my law within them, and I will write it on their hearts. And I will be their God, and they shall be my people.”
Jeremiah 31:33
“I will put my laws into their minds, and write them on their hearts, and I will be their God, and they shall be my people”
Hebrews 8:10