A.T. Robertson Commentary Luke 22:21

"But behold, the hand of him that betrayeth me is with me on the table." — Luke 22:21 (ASV)

That betrayeth (του παραδιδοντος). Present active participle, actually engaged in doing it. The hand of Judas was resting on the table at the moment. It should be noted that Luke narrates the institution of the Lord's Supper before the exposure of Judas as the traitor while Mark and Matthew reverse this order.