In the Third year of Jesus' public ministry (30 AD):

And it came to pass, as he went to Jerusalem, that he passed through the midst of Samaria and Galilee. And as he entered into a certain village, there met him ten men that were lepers, which stood afar off: and they lifted up their voices, and said, Jesus, Master, have mercy on us. And when he saw them, he said unto them, Go shew yourselves unto the priests. And it came to pass, that, as they went, they were cleansed. And one of them, when he saw that he was healed, turned back, and with a loud voice glorified God, and fell down on his face at his feet, giving him thanks: and he was a Samaritan. And Jesus answering said, Were there not ten cleansed? but where are the nine? there are not found that returned to give glory to God, save this stranger. And he said unto him, Arise, go thy way: thy faith hath made thee whole. (Luke 17)

Jews had no dealings with the Samaritans. Samaritans were looked down on because, while being Jews, they were ethnically mixed with Assyrians; and were not as religiously informed. However these ten lepers, it's safe to assume some were Jews, Luke and Jesus point out the Samaritan. Therefore while Jews and Samaritans would not walk with one another, when you become a leper that rule suddenly changes. Lepers weren't allowed in cities, so they had to live on their own in their little groups on the outside; and only then did the racial divide suddenly become useless. Ethnicity isn't going to matter on judgement day. It doesn't matter when we're covered in sin: the same as everyone else.
Jesus never said He'd cleanse the lepers, He only told them to go show themselves to the priests. By faith they went and were healed. Jesus never said stop and come back and give thanks. But the one who did is greatest. God isn't interested in robots. We get that with people who don't understand how to read the Bible, they don't read it in a personal living way but in some dry mechanical dead way. God is the God of the living. Now we have been told, thank you Jesus, take the time to thank Jesus, and don't just follow commandments for the sake of religion. But we need a relationship with the Son of God.