1 Samuel 20:42

And Jonathan said to David, Go in peace, forasmuch as we have sworn, both of us, in the name of the Lord, saying, The Lord be between me and thee, and between my seed and thy seed forever. This oath they wanted to keep with all firmness; nothing should ever persuade them to break it. And he, David, arose and departed; and Jonathan went into the city. Thus true love and friendship demonstrates its sincerity when one friend warns the other against harm and danger. And it is true in general that we should weep with those who mourn and comfort those who are in trouble, encouraging them with reference to Jehovah's mercy.