Hebrews 13:22-23
5 “And I beseech you, brethren, suffer the word of exhortation, for indeed I have written a letter unto you in few words.” Do you see that what he wrote to no one [else], he writes to them? For (he means) I do not even trouble you with long discourse.
I suppose that they were not at all unfavorably disposed towards Timothy: wherefore he also put him forward. For “know ye,” he says, “that our brother Timothy is set at liberty, with whom, if he come shortly, I will see you.” “Set at liberty,” he says; from whence? I suppose he had been cast into prison: or if not this, that he was sent away from Athens. For this also is mentioned in the Acts.
Source: Homilies on the Epistle to the Hebrews (New Advent)