The quote you're referencing is likely from the Beatitudes in the Bible, specifically from the Gospel of Luke. However, the exact wording is:
"Blessed are you who are poor, for yours is the kingdom of God." (Luke 6:20)
Matthew's version of the Beatitudes uses a slightly different wording:
"Blessed are the poor in spirit, for theirs is the kingdom of heaven." (Matthew 5:3)
There's a lot of debate about the differences between these two versions and what they mean, but generally, both verses are talking about people who are materially poor or recognize their spiritual poverty and dependence on God.