Bereshis 24:14

And let it come to pass, that the na'arah to whom I shall say, Let down thy jug, now, that I may drink; and she shall say, Drink, and I will give thy gemalim drink also; let the same be she that Thou hast appointed for Thy eved Yitzchak; and thereby shall I know that Thou hast showed chesed unto adoni.