2 Peter 1:17-18

17 For when He received honor and glory from God the Father, such an utterance as this was made to Him by the Majestic Glory, “This is My beloved Son with whom I am well-pleased” —  18 and we ourselves heard this utterance made from heaven when we were with Him on the holy mountain.

Here Peter gives validity to Jesus and what He taught them about His coming (v. 16), as he recalls when he (and James and John) saw Jesus transformed before them into a glorious state on a mountain (Matt. 17:5), and when God spoke to Him out of a cloud and said, “This is my beloved Son with whom I am well-pleased.”