KJV: 16 I will therefore chastise him, and release him. (17) For of necessity he must release one unto them at the feast.
NIV: 16 “Therefore, I will punish him and then release him. 
ESV: 16 I will therefore punish and release him.
CSB: 16 Therefore, I will have him whipped and then release him.
Pilate’s custom is introduced after Luke 23:16 from the parallel accounts.
Matthew 27:15 Now it was the governor’s custom at the festival to release a prisoner chosen by the crowd.
Mark 15:6 Now it was the custom at the festival to release a prisoner whom the people requested.