§ Of Túrin Turambar The Silmarillion

Then Morwen was distraught, and refusing the counsel of Melian she rode forth alone into the wild to seek her son, or some true tidings of him. Thingol therefore sent Mablung after her, with many hardy march-wards, to find her and guard her, and to learn what news they might; but Nienor was bidden to remain behind. Yet the fearlessness of her house was hers; and in an evil hour, in hope that Morwen would return when she saw that her daughter would go with her into peril, Nienor disguised herself as one of Thingol's people, and went with that ill-fated riding.