1 Corinthians 5:1

It is commonly reported, that there is fornication among you, and such fornication, as is not even named among the heathens, that one should have his father's wife.

James 1:6-8

But let him ask in faith, nothing doubting: for he that doubteth is like a wave of the sea, driven with the wind and tossed.

2 Peter 2:14

Having eyes full of adultery, and that cease not from sin; beguiling unstable souls, having hearts exercised with covetousness, accursed children:

2 Peter 3:16

As also in all his epistles, speaking therein of these things, in which are some things hard to be understood, which the unlearned and unstable wrest, as they do also the other scriptures, to their own destruction.

Treasury of Scripture Knowledge

Summary

Unstable as water, thou shalt not excel; because thou wentest up to thy father's bed; then defiledst thou it: he went up to my couch.

Bible References

Unstable

James 1:6
But let him ask in faith, nothing doubting: for he that doubteth is like a wave of the sea, driven with the wind and tossed.
2 Peter 2:14
Having eyes full of adultery, and that cease not from sin; beguiling unstable souls, having hearts exercised with covetousness, accursed children:
2 Peter 3:16
As also in all his epistles, speaking therein of these things, in which are some things hard to be understood, which the unlearned and unstable wrest, as they do also the other scriptures, to their own destruction.

Because

1 Corinthians 5:1
It is commonly reported, that there is fornication among you, and such fornication, as is not even named among the heathens, that one should have his father's wife.