So the king of Israel went with the king of Judah and the king of Edom. And when they had made a circuitous march of seven days, there was no water for the army or for the animals that followed them. Then the king of Israel said, “Alas! The Lord has called these three kings to give them into the hand of Moab.” And Jehoshaphat said, “Is there no prophet of the Lord here, through whom we may inquire of the Lord?” Then one of the king of Israel’s servants answered, “Elisha the son of Shaphat is here, who poured water on the hands of Elijah.” And Jehoshaphat said, “The word of the Lord is with him.” So the king of Israel and Jehoshaphat and the king of Edom went down to him. 2 Kings 3:9-12.
It is remarkable how willing Jehoshaphat, a righteous king, is to help the idolatrous king of Israel when asked. He does not play the holy separatist, refusing to partner with the wicked. But each time he does ask about the word of the Lord. He brings his faith to the table, not out of sanctimony, but as a practical matter. His trust and dependence is on the Lord.
Likewise, we should not shun our unbelieving neighbor, but bring our faith and our substance to his aid. We do what is right to bless him and win him over, so long as it does not compromise our own obedience to God.