Is there a prophetic Hadith that encourages marrying non-relatives to improve offspring and avoid hereditary diseases?

There is no authentic or acceptable evidence prohibiting or warning against marrying relatives. Rather, Allah Almighty has permitted it in His saying: "and the daughters of your paternal uncles and the daughters of your paternal aunts, and the daughters of your maternal uncles and the daughters of your maternal aunts." The Prophet, peace and blessings be upon him, married his paternal aunt's daughter and married his daughter to his paternal uncle's son.