§ Of the Fifth Battle: Nirnaeth Arnoediad The Silmarillion

Then Fingon looked towards Thangorodrim, and there was a dark cloud about it, and a black smoke went up; and he knew that the wrath of Morgoth was aroused, and that their challenge was accepted. A shadow of doubt fell upon Fingon's heart; and he looked eastwards, seeking if he might see with elven-sight the dust of Anfauglith rising beneath the hosts of Maedhros. He knew not that Maedhros was hindered in his setting-forth by the guile of Uldor the accursed, who deceived him with false warnings of assault from Angband.