The prophet Joel predicted the outpouring of the Holy Spirit. Specifically, Joel 2:28-29 says:
"And it shall come to pass afterward, that I will pour out my Spirit on all flesh; your sons and your daughters shall prophesy, your old men shall dream dreams, and your young men shall see visions. Even on the male and female servants in those days I will pour out my Spirit."
This prophecy is directly referenced by the Apostle Peter in Acts 2:16-21 to explain the events of Pentecost, when the Holy Spirit was poured out on the believers in Jerusalem.