While Jesus was having dinner at Matthew's house, many tax collectors and "sinners" came and ate with him and his disciples.
When the Pharisees saw this, they asked his disciples, "Why does your teacher eat with tax collectors and 'sinners'?"1
References for Matthew 9:11
On hearing this, Jesus said, "It is not the healthy who need a doctor, but the sick.
But go and learn what this means: 'I desire mercy, not sacrifice.'2 For I have not come to call the righteous, but sinners."3
References for Matthew 9:13