I saw my daughter send a letter to some boy her age
Who locked up
First I regretted it then caught my rage like
How could I not protect her from this awful phase

from Nas – Daughters Lyrics on Rap Genius

Meaning

History is repeating itself — when Nas was about her age, he wrote “One Love”, about him writing one of his friends in jail — now his daughter is doing the exact same thing.

He wants a better life for her, hence he “caught his rage” meaning he had to contain his anger before he could speak to her.

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