To him they agreed (epeisthēsan autōi). First aorist passive indicative of peithō, to persuade, the passive to be persuaded by, to listen to, to obey. Gamaliel’s shrewd advice scored as against the Sadducaic contention (Act 5:17).
Not to speak (mē lalein). The Sanhedrin repeated the prohibition of Act 4:18 which the apostles had steadily refused to obey. The Sanhedrin stood by their guns, but refused to shoot. It was a “draw” with Gamaliel as tactical victor over the Sadducees. Clearly now the disciples were set free because only the Sadducees had become enraged while the Pharisees held aloof.