Shulchan Arukh Yoreh De'ah · Siman 270

English

There is a Positive Commandment on every Jewish man to copy a Torah Scroll for himself. Even if his ancestors bequeathed one to him, he is still commanded to copy one of his own. He is not permitted to sell it even if he owns many Torah Scrolls. This is even if he does not have what to eat. (A Torah Scroll can be sold] only under the most dire circumstance)(Haghoth Maimoni Chapter 6). Even selling an old [Torah Scroll] in order to buy a new [Torah Scroll] is forbidden. However [if the scroll is sold in order to acquire funds] to study Torah or to marry a woman the sale is permitted if the seller has nothing else to sell. Rema: For redeeming Jewish captives it is permitted to sell [a Torah Scroll] (See Tosfoth Bava Bathra chapter 1 beginning with "ואגודה שם", and Orah hayim 153). [If] he hired a scribe to copy a Torah Scroll for him or [If] he bought [a Torah Scroll] with copying errors and he proofread it, it is as if he copied [the Torah Scroll] himself (Beith Yosef quoting Nimukei Yosef). However [if] he bought it as is [with errors] and did not proofread it at all, it is like he abducted a Mitzva from the market and he does not fulfill his obligation [of copying a Torah Scroll] (Tur quoting Rabbi Yehoshua ben Levi from Menahoth chapter 2)

English

Nowadays the commandment is to copy the five books of Moses, the Mishna, and the Talmud with its commentaries. [These books] can only be sold [in order to gather funds] to study Torah or to marry a woman.