The case of nezirut Shimshon involves a person who specifically states that he wants to accept upon himself this type of nezirut. Unlike someone who accepts standard nezirut, a nazir Shimshon is allowed to come into contact with the dead. Unlike someone who accepts nezirut for his entire life, a nazir Shimshon can never cut his hair. The Sages had a tradition that nezirut Shimshon was also unique in that the person who comes to regret having accepted this nezirut cannot be released from his obligation by the Sages. Rashi suggests that the source for this is the fact that Shimshon himself did not choose to be a nazir, rather the condition was imposed on him by a heavenly angel. Thus, Shimshon could not escape his fate as a nazir, and neither can someone who bases his own nezirut on the model of Shimshon.
According to most of the commentaries, it is not clear whether the person who says, “I will be like Moshe on the seventh day of Adar,” has, in fact, accepted nezirut.
We can probably assume that on the day of his death, many of his followers in the desert accepted upon themselves nezirut as a symbol of mourning for their great leader, since many of the laws of nezirut – for example, not cutting hair or drinking wine – mirror basic laws of aveilut. On the other hand, perhaps this statement is a reference to the day that Moshe was born, which was certainly a day of celebration, or, at any rate, was not a day that he accepted upon himself nezirut or other prohibitions. Another approach suggested by Rashi is that the person may be viewed as saying that just as Moshe did not drink wine on the day of his death, similarly he is accepting upon himself nezirut.