وَالفَجْرِ

وَالْفَجْرِ is a phrase (شِبْهُ الجُمْلَةِ) consisting of a particle of pulling down (a preposition) and a genitive noun

Phrase		Particle / Noun		Noun		Particle
شِبْهُ الجُمْلَةِ		جَارٌ وَمَجْرُوْرٌ		اسْمٌ مَجْرُوْرٌ		حَرْفُ جَرٍّ
Phrase		Compound		Genitive Noun		Particle of pulling down/Preposition

by the dawn	–	وَالْفَجْرِ	=	الْفَجْرِ	+	وَ
		by the dawn		the dawn		by

Surah/	Below is the only verse in the holy Quran containing the compound	وَالفَجْرِ
Verse

89-1	By the dawn	وَالفَجْرِ

Valuable resources:

Dictionary of the holy Quran by Abdul Mannan Omar