Imam Fakhr-ud-Deen Raazi رَحْمَةُ الـلّٰـهِ عَلَيْه states in ‘Tafseer-e-Kabeer’: The meaning of ‘وَ الضُّحٰی’ is ‘by the luminous face of Mustafa صَلَّى الـلّٰـهُ عَلَيْهِ وَاٰلِهٖ وَسَلَّم’, and the meaning of ‘وَ الَّیۡل’ is ‘by his black tresses.’ (Tafseer-e- Kabeer, vol. 11, p. 191)

صَلُّوۡا عَلَى الۡحَبِيۡب       صَلَّى اللّٰهُ عَلٰى مُحَمَّد

Dear Islamic brothers! Ponder over how beautifully Allah Almighty has taken an oath by the shining face and beautiful hair of the Beloved Prophet صَلَّى الـلّٰـهُ عَلَيْهِ وَاٰلِهٖ وَسَلَّم; not only this, Allah Almighty has also mentioned an oath by the speech of His Beloved صَلَّى الـلّٰـهُ عَلَيْهِ وَاٰلِهٖ وَسَلَّم and by various things that are linked to him. Let us listen to them:

Allah Almighty mentions an oath by the speech of His Beloved صَلَّى الـلّٰـهُ عَلَيْهِ وَاٰلِهٖ وَسَلَّم and states:

وَ قِیْلِهٖ یٰرَبِّ اِنَّ هٰۤؤُلَآءِ قَوْمٌ لَّا یُؤْمِنُوْنَۘ(۸۸)

And I swear by this saying of the Messenger; that,
 ‘O my Lord! These people do not believe.’

[Kanz-ul-Iman (translation of Quran)] (Part 25, Surah Al-Zukhruf, Verse 88)

Allah Almighty takes an oath by the blessed city of His Beloved صَلَّى الـلّٰـهُ عَلَيْهِ وَاٰلِهٖ وَسَلَّم and states: