John Gill Commentary Genesis 20:6

"And God said unto him in the dream, Yea, I know that in the integrity of thy heart thou has done this, and I also withheld thee from sinning against me. Therefore suffered I thee not to touch her." — Genesis 20:6 (ASV)

And God said to him in a dream
The same dream continued: also ,
or "also" I know that you did this in the integrity of your heart ;
not only you know, but I, who know all things, know and acknowledge that this was so done by you. Abimelech's plea is admitted, and a very great testimony borne to his integrity in this matter; and throughout the whole account he appears to be a man of great honour and uprightness, especially in this affair, if not a good man:

for I also withheld you from sinning against me ;
for had he committed adultery with her, it has been not only a sin against her, and against her husband, but against God being contrary to his will revealed in the minds of men by the law and light of nature, before the law of Moses was given: and indeed all sin against the neighbour is ultimately against God, see (Psalms 51:4) ;

and now from the commission of this sin God restrained Abimelech, either by some impulse upon his mind not to take her to be his wife as yet, or by throwing some thing or other in the way of it, in his providence, or by inflicting some disease upon him, which rendered him incapable of it, (Genesis 20:17) ; therefore suffered I you not to touch her ;
that is, to have carnal knowledge of her, see (1 Corinthians 7:1) ; as there is nothing done but what is done by divine permission, so many more evils would be committed than there are, were it not that men are restrained from them by the power and providence of God, not suffering them to do them; and in particular this sin was prevented, that it might not in any respect be a doubtful point whether Isaac, whom Sarah had now conceived, was a legitimate son of Abraham; and these expressions of Abimelech not coming near her, (Genesis 20:4) ; and not touching her as here, are used for that purpose.