תּלמוד אויף דברי הימים א 3:2

Can these [verses] be compared? There [in Numbers,] it is Canaan. Here [in Deuteronomy], it is Sichon. It is taught: He who is Sichon, is Arad, and is Canaan. He is Sichon, for he is similar to a colt [si'ach] in the desert. He is Canaan, for the name of his kingdom. And what is his [real] name? Arad is his name. Alternatively: He is Arad, for he is similar to a wild donkey [arud] in the desert. He is Canaan, for the name of his kingdom. And what is his [real] name? Sichon is his name.

Rather, Rabbi Elazar said, '[Learn the proof for Nissan] from here: (I Chronicles 3:2) "And he began to build in the 2nd month, on the 2nd, in the 4th year of his kingship." What is "[on the] 2nd"? Is it not the second month from when they [began to] count his [years of] kingship?

And it says, (Numbers 10:11) "And it was in the 2nd month of the 2nd year..." And it says, (Exodus 19:1), "And it was in the 3rd month from when the Israelites left the land of Egypt..." And it says, (I Chronicles 3:2) "And he began to build..."