The promise which Peter has in mind is the one found in Isaiah 65:17 and repeated in Isaiah 66:22: Behold, I will create new heavens and a new earth.
1 Hope of a new creation is also found elsewhere in the New Testament (Romans 8:19–21; Revelation 21:1).
13 But according to his promise we are waiting for new heavens and a new earth in which righteousness dwells.