In The Children of Húrin:
It is said that for a while the sons of Galdor dwelt in Brethil as foster-sons of Haldir their uncle, after the custom of Northern men in that time. They often went...
In The Silmarillion, “Of the Ruin of Beleriand”:
Thus it was that the sons of Galdor were fostered in Brethil by Haldir their uncle, according to the custom of Men in that time; and they went . . .