A.T. Robertson Commentary Acts 4:3

"And they laid hands on them, and put them in ward unto the morrow: for it was now eventide." — Acts 4:3 (ASV)

In ward (εις τηρησιν). Probably in one of the chambers of the temple. In safe keeping (from τηρεω, to guard). Old word, in the N.T. only here and Ac 5:18; 1 Corinthians 7:19. So in papyri.

Now eventide (εσπερα ηδη). Hence no trial could take place before the next day, a regulation violated in the case of Jesus.