Acts 18:25
This man was instructed in the way of the Lord; and being fervent in the spirit, he spake and taught diligently the things of the Lord, knowing only the baptism of John.
Cross-reference
Acts 18:28 shows the result: Apollos powerfully refuted Jews using Scripture, building on the accurate teaching noted in verse 25.
Acts 19:3 shows other disciples also only knew John's baptism, directly paralleling Apollos' limited knowledge and preparing for the same correction.
In Acts 19:9, Paul faces opposition while teaching the Way — the same term for Christianity that Apollos taught, now met with stubborn unbelief.
In Acts 19:23, the Way causes a great disturbance in Ephesus — the same movement Apollos knew and taught, now provoking conflict.
John 1:19-36 presents John the Baptist's testimony about Jesus, exactly the message Apollos knew and taught.
Romans 12:11 uses the exact phrase 'fervent in spirit' — a direct parallel to Apollos' described character.