Nazir 23 - 29
Rav Yehuda said in the name of Rav, “One should always be involved in learning Torah and fulfilling mitzvot even if not for the purest reasons, because this will lead to learning and fulfilling for pure reasons.”
An important caveat: This encouragement applies to motives of personal gain; but one who learns Torah as a means to gain knowledge to try to refute or degrade it is “better off unborn”. (Tosefot)
- Nazir 23b
“In the reward of the forty-two sacrifices that the wicked Balak offered, he merited that Ruth would be descended from him.”
This is an example of the ruling of Rav Yehuda in the name of Rav that it is a positive measure to fulfill a mitzvah even if it is only for personal motive. The gemara explains Ruth’s lineage from the king of Moav as follows: Rabbi Yossi the son of Rabbi Chanina said, “Ruth was the daughter of the son of Eglon, the king of Moav”.
- Nazir 23b