Musar על אבות 3:8

We further find in Avoth (3:8): "R. Meir says: 'If one forgets a single thing from his learning, Scripture accounts it to him as if he is liable for his soul, as it is written (Devarim 4:9): "Only take heed to yourself, and heed your soul exceedingly, lest you forget, etc."

And [(by neglecting Torah study)] he especially injures himself, as Chazal have said: "Whoever forgets one item of his learning brings bout exile to his sons, as it is written (Hoshea 4:6): 'And you have forgotten the Torah of your G-d — I, too, will forget your sons.'"