אבניה ברזל. א"ר אבא, כל תלמיד חכם שאינו קשה כברזל אינו ת"ח, שנאמר ארץ אשר אבניה ברזל, אל תקרא אבניה אלא בוניה
English: R’ Abba said: Any Torah scholar who is not as hard as iron is not a [true] Torah scholar, as it is said, “a land whose stones are iron” — do not read “avaneha” (its stones) but “boneha” (its builders).
On the daf / in context: Taanit 10a.
Type of Learning
Custom (wordplay — stones / builders)
What Is Learned
A talmid chacham must have iron firmness; the “builders” of the Land are its scholars.