Мидраш к Мидот 2:12

When the Temple was destroyed, the sages instituted (the rule) that the bridegrooms and mourners should go to the synagogues and to the houses of study. The men of the place see the bridegroom and rejoice with him; and they see the mourner and sit with him upon the earth, so that all the Israelites may discharge their duty in the service of loving-kindness. With reference to them he says: Blessed art Thou, who giveth a good reward to those who show loving-kindness.