The second condition of bai‘at also includes a commitment to avoid adultery. In this respect, Almighty Allah says in the Holy Qur’an:1
And come not near unto adultery; surely, it is a foul thing and an evil way.
In a hadith, Muhammad Bin Sirin narrates that the Holy Prophet(sa) admonished to do the following. Then he narrates a long hadith that includes the admonition that chastity and truthfulness are better and everlasting in contrast to adultery and falsehood (Sunanud-Darimiyyi, Kitab-ul-Wasaya, Babu ma yustahabbu bil-wasiyyati minat-tashahhudi wal kalam)
Here adultery and falsehood have been mentioned together. This also illustrates how major a sin lying is.
The Promised Messiah(as) says:
Do not go near adultery. That is to say, avoid all occasions that create that thought in your mind. Avoid all ways that carry a risk of getting involved in this sin. Whoever commits adultery goes to the limit of the evil. Adultery is a very evil way. It stops you from reaching your true objective and carries major risks in it. He who is unable to get married should try to maintain his chastity in other ways; for instance, he should keep fasts or reduce his food intake, or should do hard physical work. (Islami Usul ki Philosophy, Ruhani Khaza’in, vol. 10, p. 342)
The Promised Messiah(as) has admonished to stay away from things that lead to adultery. Sometimes the youth ignore this matter. They get used to watching films that are not fit to be seen. They are beneath good moral standards. Avoid them because that is also a form of adultery.
1 Bani Isra’il, 17:33