@joshan.daniel2 You know your uncle better than I do and you also heard the words, so my response may be off target. If I am off target, please feel free to help me to correct course.
If someone were to say, “X is OT doctrine and not NT,” to me, I would first respond with an interested look on my face, “Really? What are your reasons for saying that?” This question expresses my desire to listen to the other person and gracefully assumes that the person has examined the issue enough to have multiple reasons for the opinion. How the person answers my question would guide the course of the conversation.
Assuming that your uncle is not looking for a quarrel, he needs to clarify what he means by “doctrine.” In theology, doctrine is a set of beliefs that guides behavior. Doctrine is not law. Law expresses doctrine. A doctrine can be stated as a fact, such as, “I am the LORD your God, who brought you out of the land of Egypt, out of the house of slavery” (Exodus 20:2, ESV). The following Ten Commandments express that doctrine, but they are not doctrine. The same can be said of almost the entire corpus of OT law.
Tithing in the OT really stems from a tradition that Abraham started when he tithed to Melchizedek (Genesis 14:18-20). Abraham did not tithe as an end in itself. He tithed because he believed that Melchizedek was working in God’s service. Abraham expressed his love for “God Most High, Possessor of heaven and earth” (Genesis 14:22b, ESV) through tithing. All forms of OT offering, including tithing, were intended to express this same love for God and the advancement of Heaven’s cause. These were not doctrines in themselves.
Fast forward to the NT. Tithing is expected, but never required. The nascent church gave “as any had need” (Acts 2:45b, ESV). People sold property and gave the proceeds to the Christian community (Acts 4:32-37). When Ananias sold some property and gave only part of the proceeds, Peter said, “While it remained unsold, did it not remain your own? And after it was sold, was it not at your disposal?” (Acts 5:4, ESV) This implies that Ananias was not required to bring anything. The Spirit killed him not for being “stingy,” but for lying about what he brought.
Nevertheless Paul writes in 1 Timothy 5:17-18:
Let the elders who rule well be considered worthy of double honor, especially those who labor in preaching and teaching. For the Scripture says, “You shall not muzzle an ox when it treads out the grain,” and, “The laborer deserves his wages.” (ESV)
He also writes about his personal policy not to take advantage of his right as an apostle to be paid for his work:
Who serves as a soldier at his own expense? Who plants a vineyard without eating any of its fruit? Or who tends a flock without getting some of the milk? …If we have sown spiritual things among you, is it too much if we reap material things from you? If others share this rightful claim on you, do not we even more? Nevertheless, we have not made use of this right…" (1 Corinthians 9:7, 11-12a, ESV)
Jesus pointed out that the poor widow gave much more with her mite than the rich people who gave of their excess (Mark 12:41-44). We tithe more than ten percent. We tithe from our hearts. Our tithe expresses our love for God and neighbor.