The word فجر in the Quran

أُحِلَّ لَكُمْ لَيْلَةَ ٱلصِّيَامِ ٱلرَّفَثُ إِلَىٰ نِسَآئِكُمْ هُنَّ لِبَاسٌ لَّكُمْ وَأَنتُمْ لِبَاسٌ لَّهُنَّ عَلِمَ ٱللَّهُ أَنَّكُمْ كُنتُمْ تَخْتَانُونَ أَنفُسَكُمْ فَتَابَ عَلَيْكُمْ وَعَفَا عَنكُمْ فَٱلْـَٰٔنَ بَٰشِرُوهُنَّ وَٱبْتَغُوا۟ مَا كَتَبَ ٱللَّهُ لَكُمْ وَكُلُوا۟ وَٱشْرَبُوا۟ حَتَّىٰ يَتَبَيَّنَ لَكُمُ ٱلْخَيْطُ ٱلْأَبْيَضُ مِنَ ٱلْخَيْطِ ٱلْأَسْوَدِ مِنَ ٱلْفَجْرِ ثُمَّ أَتِمُّوا۟ ٱلصِّيَامَ إِلَى ٱلَّيْلِ وَلَا تُبَٰشِرُوهُنَّ وَأَنتُمْ عَٰكِفُونَ فِى ٱلْمَسَٰجِدِ تِلْكَ حُدُودُ ٱللَّهِ فَلَا تَقْرَبُوهَا كَذَٰلِكَ يُبَيِّنُ ٱللَّهُ ءَايَٰتِهِۦ لِلنَّاسِ لَعَلَّهُمْ يَتَّقُونَ ۝١٨٧

It has been made permissible for you the night preceding fasting to go to your wives [for sexual relations]. They are a clothing for you and you are a clothing for them. Allāh knows that you used to deceive yourselves, so He accepted your repentance and forgave you. So now, have relations with them and seek that which Allāh has decreed for you [i.e., offspring]. And eat and drink until the white thread of dawn becomes distinct to you from the black thread [of night]. Then complete the fast until the night [i.e., sunset]. And do not have relations with them as long as you are staying for worship in the mosques. These are the limits [set by] Allāh, so do not approach them. Thus does Allāh make clear His verses [i.e., ordinances] to the people that they may become righteous.

أَقِمِ ٱلصَّلَوٰةَ لِدُلُوكِ ٱلشَّمْسِ إِلَىٰ غَسَقِ ٱلَّيْلِ وَقُرْءَانَ ٱلْفَجْرِ إِنَّ قُرْءَانَ ٱلْفَجْرِ كَانَ مَشْهُودًا ۝٧٨

Establish prayer at the decline of the sun [from its meridian] until the darkness of the night and [also] the Qur’ān [i.e., recitation] of dawn. Indeed, the recitation of dawn is ever witnessed.

يَٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوا۟ لِيَسْتَـْٔذِنكُمُ ٱلَّذِينَ مَلَكَتْ أَيْمَٰنُكُمْ وَٱلَّذِينَ لَمْ يَبْلُغُوا۟ ٱلْحُلُمَ مِنكُمْ ثَلَٰثَ مَرَّٰتٍ مِّن قَبْلِ صَلَوٰةِ ٱلْفَجْرِ وَحِينَ تَضَعُونَ ثِيَابَكُم مِّنَ ٱلظَّهِيرَةِ وَمِنۢ بَعْدِ صَلَوٰةِ ٱلْعِشَآءِ ثَلَٰثُ عَوْرَٰتٍ لَّكُمْ لَيْسَ عَلَيْكُمْ وَلَا عَلَيْهِمْ جُنَاحٌۢ بَعْدَهُنَّ طَوَّٰفُونَ عَلَيْكُم بَعْضُكُمْ عَلَىٰ بَعْضٍ كَذَٰلِكَ يُبَيِّنُ ٱللَّهُ لَكُمُ ٱلْـَٔايَٰتِ وَٱللَّهُ عَلِيمٌ حَكِيمٌ ۝٥٨

O you who have believed, let those whom your right hands possess and those who have not [yet] reached puberty among you ask permission of you [before entering] at three times: before the dawn prayer and when you put aside your clothing [for rest] at noon and after the night prayer. [These are] three times of privacy for you. There is no blame upon you nor upon them beyond these [periods], for they continually circulate among you - some of you, among others. Thus does Allāh make clear to you the verses [i.e., His ordinances]; and Allāh is Knowing and Wise.

وَٱلْفَجْرِ ۝١

By the dawn

سَلَٰمٌ هِىَ حَتَّىٰ مَطْلَعِ ٱلْفَجْرِ ۝٥

Peace it is until the emergence of dawn.