Acts 2:1-4:

And when the day of Pentecost was fully come, they were all with one accord in one place. And suddenly there came a sound from heaven as of a rushing mighty wind, and it filled all the house where they were sitting.
And there appeared unto them cloven tongues like as of fire, and it sat upon each of them.
And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance.

See also:

How to Be Baptized with the Holy Spirit
The Kingdom of God Is Here NOW
Power, Then and Now
What Romans 8:9 Really Means
Baptism with the Spirit and Being Filled with the Spirit
Objection: Mark 16:9-20 Was Not in Some Early Manuscripts
Notes on Acts 1:8