Hebrews 6:4

6:4 For it is impossible in the case of those who have once been enlightened, tasted the heavenly gift, become partakers of the Holy Spirit,

Hebrews 11:6

11:6 Now without faith it is impossible to please him, for the one who approaches God must believe that he exists and that he rewards those who seek him.

Hebrews 6:18

6:18 so that we who have found refuge in him may find strong encouragement to hold fast to the hope set before us through two unchangeable things, since it is impossible for God to lie.