Talmud Bavli Menachot on the Mitzvah to Write a Torah Scroll

"And Rabbi Yehoshua bar Abba said in the name of Rav Gidel, who said in the name of Rav: One who buys a Torah scroll from the market is like on who grabs a mitzvah from the market.  If he wrote it himself, Scripture considers him as if he received it personally from Mount Sinai."

-- Talmud Bavli, Menachot 30a

"And now write for yourselves this song, and teach it to the Children of Israel, place it in their mouths."

-- Deuteronomy 31:19