Hebrews 13:23

Know ye that [our] brother Timothy is set at liberty
This is the same person to whom the Apostle Paul wrote two epistles, and whom he often calls his son, though sometimes his brother, as here, ( Colossians 1:1 ) ( 1 Thessalonians 3:2 ) of him he says, that he was set at liberty, or "dismissed"; either by the apostle, by whom he was sent into some parts, upon some business; or rather was loosed from his bonds, having been a prisoner for the sake of Christ and the Gospel; and, it may be; a fellow prisoner with the apostle, at Rome, as Aristarchus and others were; and this very great and useful person being known, very likely, to the Hebrews, since his mother was a Jewess, and he himself was well reported of by the brethren at Lystra and Iconium, ( Acts 16:1 Acts 16:2 ) it was a piece of good news to them to hear of his release:

with whom, if he come shortly, I will see you;
by which it seems that Timothy was now absent from the apostle, but that he expected him to come in a short time; when, if he should, they would both come together, and visit the Hebrews; which looks as if the apostle was at liberty himself, or at least had some hopes of his deliverance from prison; but whether he ever had his liberty after this, and saw the Hebrews any more, cannot be said; the contrary seems most probable.