JOEL - Four times. The Father introduced His Son at the baptism of Jesus:
Matt 3:17
Mark 1:11
Luke 3:22
D&C 93:15

At the mount of transfiguration:
Matt 17:5
Mark 9:7:
Luke 9:35:
2 Peter 1:17

When Jesus appeared to the Nephites::
3 Nephi 11:7

When Jesus appeared to Joseph Smith::
Joseph Smith History 1:17