الفَجْرِ

A word in the Arabic language will either be 1) a verb or 2) a noun or 3) a particle – الفَجْرِ is a noun

A noun may either be 1) Definite or indefinite 2) Masculine or feminine 3) Singular, dual or plural 4) Nominative, accusative or genitive

الفَجْرُ is the natural state of this definite noun and it changes to الفَجْرِ due to: 1) a preposition that precedes it or 2) a possessed noun that precedes it or 3) it’s a noun of dependent declension a) نَعْتٌ / صِفَطٌ adjectives b) التَّوْكِيْدُ emphatic c) المَعْطُوْفٌ conjunction d) البَدَلُ synonym

Surah/Below are the 5 verses in the holy Quran containing 6 occurrences of the definite, genitive nounالفَجْرِ
Verse
It is permitted for you on the nights of fasting to approach your wivesأُحِلَّ لَكُمْ لَيْلَةَ الصِّيَامِ الرَّفَثُ إِلَى نِسَآئِكُمْ
They are a covering for you and you are a covering for themهُنَّ لِبَاسٌ لَّكُمْ وَأَنْتُمْ لِبَاسٌ لَّهُنَّ
Allah (SWT) knows that you used to deceive yourselves so, He turned towards you and forgave youعَلِمَ اللهُ أَنَّكُمْ كُنْتُمْ تَخْتَانُوْنَ أَنْفُسَكُمْ فَتَابَ عَلَيْكُمْ وَعَفَا عَنْكُمْ
so now have relations with them and seek what Allah (SWT) has ordained for youفَالْئَانَ بَاشِرُوْهُنَّ وَابْتَغُوْا مَا كَتَبَ اللهُ لَكُمْ
so, eat and drink until the white thread appears distinct to youوَكُلُوْا وَاشْرَبُوْا حَتَّى يَتَبَيَّنَ لَكُمُ الخَيْطُ الأَبْيَضُ
from the black thread of dawn then complete your fast till the nightمِنَ الخَيْطِ الأَسْوَدِ مِنَ الفَجْرِ ثُمَّ أَتِمُّوْا الصِّيَامَ إِلَى الَّيْلِ
and do not have relations with them while you are secluded in the mosquesوَلَا تُبَاشِرُوهُنَّ وَأَنْتُمْ عَاكِفُوْنَ فِي المَسَاجِدِ
These are the limits set by Allah (SWT) so do not approach themتِلْكَ حُدُوْدُ اللهِ فَلَا تَقْرَبُوهَا
2-187Thus does Allah (SWT) make clear His ordinances to mankind so that they may become righteousكَذَلِكَ يُبَيِّنُ اللهُ ءَايَاتِهِ لِلنَّاسِ لَعَلَّهُمْ يَتَّقُوْنَ
17-78
24-58
89-1By the dawnوَالفَجْرِ
97-5Peace it is until the emergence of dawnسَلَامٌ هِيَ حَتَّى مَطْلَعِ الفَجْرِ