ועתה כתבו לכם את השירה הזאת (וילך לא:יט)

A Sefer Torah was once found abandoned in an open field, and doubts arose whether the sofer (scribe) who wrote it was properly certified. If he had not been, the halachic ruling would be that such a Sefer Torah must be hidden away and not used.

The question was presented to Hagaon Reb Akiva Eiger zt’’l. He answered with an insightful approach: It is the long-standing minhag Yisrael that when completing a Sefer Torah, distinguished individuals are honored to write the final letters. Usually, each person inscribes the letter corresponding to the first letter of their name—for example, a “מ” for Moshe, etc. Understandably, the letters at the end are written in different styles, since each hand is unique.

Therefore, Reb Akiva Eiger explained, if a devout and trustworthy sofer wrote the Sefer Torah, this custom surely would have been observed. By examining the final verses, one can see a variety of handwriting styles, which is proof that the Torah was written correctly. But if the writing is perfectly uniform, it indicates the sofer wrote it all himself, and if he was unfit, then the Sefer Torah must indeed be hidden.

A gadol once repeated this story in jest and added: “מנהג ישראל תורה הוא”—the very fact that they were careful with a minhag Yisrael is itself a strong proof that the Torah scroll is kosher!