Judges 15:20
And he judged Israel in the days of the Philistines twenty years.
Cross-reference
Judges 13:1
Historical context
Judges 13:1 explains the 40-year Philistine oppression that frames Samson's 20-year judgeship mentioned here.
Judges 13:5
Prophetic fulfillment
Judges 13:5 prophesies Samson would begin to save Israel from Philistines — his 20-year judgeship here fulfills that.
Judges 16:31
Parallel
Judges 16:31 repeats that Samson judged Israel twenty years, bookending his career with the same summary.
Genesis 49:16
Prophetic fulfillment
In Genesis 49:16, Jacob prophesies Dan will judge; Samson, a Danite, fulfills this as a judge over Israel.