While much has been said or written on the subject, the best place to look for sound teaching on generosity is the Bible. Both Old and New Testaments teach generosity as a way of life for God's redeemed people, not as a rote duty but as a joyful response to God's saving grace.
WE MUST WITHHOLD NOTHING FROM THE GOD WHO GIVES EVERYTHING
This is how we know what love is: Jesus Christ laid down his life for us. And we ought to lay down our lives for our brothers. If anyone has material possessions and sees his brother in need but has no pity on him, how can the love of God be in him? Dear children, let us not love with words or tongue but with actions and in truth. This then is how we know that we belong to the truth, and how we set our hearts at rest in his presence ... 1 John 3:16-19