I indeed baptize you with water unto repentance: but he that cometh after me is mightier than I, whose shoes I am not worthy to bear: he shall baptize you with the Holy Ghost, and with fire: Matthew 3:11
In this verse Baptism of Holy Spirit refers to the day of Pentecost; Acts 2:4 clarifies the baptism of Holy Ghost (to believers JEWS first) and baptising of fire refers to judgement day.
Looking in to verse 12,
Whose fan is in his hand, and he will throughly purge his floor, and gather his wheat into the garner; but he will burn up the chaff with unquenchable fire. Matthew 3:12
Jesus Christ is referring as fan and grains to true believers who will be carried into the barn and chaff is referred to unbelievers who are gathered and burned with unquenchable fire. Verse 12 refers to judgement by reading in reference to verse 11.
Baptism with fire refers to judgement day.