Moses went up to the mountain top to receive the “Ten Commandments” on Pentecost and was there for 40 days and 40 nights. Following that, he came down the mountain on the 9th of Av (Jewish Black Fast Day that the two temples have been destroyed on) and broke the tablets with the commandments on them.
Jesus was baptized by John in the Jordan River and then went into the wilderness for 40 days and 40 nights and then Satan said “cast yourself from the temple”.
Given the parallel between these two events, it appears that Jesus was baptized on Pentecost. Thus because God is the same yesterday, today and forever, we can see the precedent of baptism in Acts Chapter 2 on Pentecost. If Christ was baptized on Pentecost, how appropriate for the first baptism with the Holy Spirit to have been on Pentecost.