The Mishna states that an ordinary time period for Nezirus is thirty days, so if one does not state specifically for how long he wishes to be a Nazir, he is required to fulfill the minimum thirty day period of Nezirus. The Gemara derives this ruling from the word יהיה which is said regarding a Nazir, and the word יהיה equals in gematria thirty. It is noteworthy that the word שלשים, thirty, equals in gematria the word בהנזירות, in the state of being a Nazir.
The Gemara states that a nedavah for nezirus is regarded as virtuous in cases such that of Shimon HaTzadik, as the Baraisa states: Shimon HaTzadik said, “I never ate from the meat of an asham sacrifice offered by a nazir who had become tamei except for one case. A handsome young man from the south with beautiful eyes and locks of hair arranged in curls (who had become tamei and came to the Bais HaMikdash to have his hair removed and to offer the required sacrifice) came to me, and I asked him why he was prepared to shave off his beautiful hair (he had taken upon himself a vow to become a nazir, which would eventually lead to having such beautiful hair removed, and(even if he would have completed his term of nezirus without becoming tamei, a nazir shaves his head upon completion). He responded to me, ‘I was a shepherd for my father and one day I went to a spring to draw water and I witnessed my reflection in the water. My evil inclination suddenly atteneopted to seduce me by using my good looks for an immoral act, and wished to drive me out from this world. I said to my evil inclination: Wicked one! Why are you being so haughty in a world that is not yours, with one that in the future will be worms and maggots? I swore at that time to become a nazir.’ Shimon HaTzadik declared, ‘I was so impressed (by his piety) that I kissed him on his head and said to him, May there be more vowers of nezirus like you in Israel.”
The Gemara states that the Nazir came from the south, as the Gemara (Bava Basra 25b) states that one who wishes to gain wisdom should pray southward. Thus, the Nazir was “outsmarting” his Evil Inclination. Alternatively, the south alludes to the left, i.e the forces of evil who wish to destroy a person spiritually, so the Nazir specifically came from the “south,” as he “fought fire with fire,” and instead of shaving his hair immediately, he channeled his beautiful locks towards heaven.
Daf Drush 