Who said "A man is sworn to the Watch"?

This quote is attributed to Jon Snow.

A man is sworn to the Watch - Jon Snow

"A man is sworn to the Watch"

Jon Snow

Character in A Storm of Swords

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"A man must know how to die"

"The night gathers, and now my watch begins"

"I shall wear no crowns and win no glory"

"I am of the night."