Which respected Pharisee advised the Sanhedrin to leave the apostles alone?

Answer: Gamaliel

Gamaliel, a teacher of the law, said if their work was of human origin it would fail, but if from God they could not stop it.

“But a Pharisee named Gamaliel, a teacher of the law who was honored by all the people, stood up in the Sanhedrin and ordered that the men be put outside for a short time.”— Acts 5:34 (BSB)