Messiah Yeshua said
in the Sermon on the Mount:
Matt 5:27 You have heard that it was said by them of old time, Thou shalt
not commit adultery:
Matt 5:28 But I say unto you, That whosoever looketh on a woman to lust
after her hath committed adultery with her already in his heart.
We see the prohibition of the adultery in the first book of Torah already:
Gen 2:24 Therefore shall a man leave his father and
his mother, and shall cleave unto his wife: and they shall be one flesh.
Let us read these words once more: "shall
cleave unto his wife".
In Tanach we read:
Job 24:15 The eye also of the adulterer waiteth for the twilight, saying, No eye shall see me: and disguiseth [his] face.
What did Pharisees
teach about this question?
"One who gazes lustfully upon the small finger of a married woman, it is
as if he has committed adultery with her." (Babylonian Talmud, Kallah, Ch.
1)
(http://www.yashanet.com/studies/matstudy/mat6c.htm)
"One can commit adultery not only with one's body, but even with one's
eyes." (Vayikra Rabbah, Ch.23) (Winkler, 1998, p. 234)
"... do not talk much with women. This was said about one's own wife; how
much more so about the wife of one's neighbor. Therefore the sages have said:
He who talks too much with women brings evil upon himself and neglects the
study of the Torah and will in the end inherit Gehenna." (Pirkei Avot 1:5)
(http://www.shechem.org/torah/avot.html)
Rabbi Shaul said:
1Cor 7:2
Nevertheless, [to avoid] fornication, let every man have his own wife,
and let every woman have her own husband.
1Thess 4:3
For this is the will of God, [even] your sanctification, that ye should
abstain from fornication: