Acts 1:4-5 New International Version (NIV)

4 On one occasion, while he was eating with them, he gave them this command: “Do not leave Jerusalem, but wait for the gift my Father promised, which you have heard me speak about. 5 For John baptized with water, but in a few days you will be baptized with the Holy Spirit.”

Acts 2:1-4 New International Version (NIV)

2 When the day of Pentecost came, they were all together in one place.2 Suddenly a sound like the blowing of a violent wind came from heaven and filled the whole house where they were sitting. 3 They saw what seemed to be tongues of fire that separated and came to rest on each of them. 4 All of them were filled with the Holy Spirit and began to speak in other tongues as the Spirit enabled them.