Assalaamu alaykum wa rahmatullaahi wa barakaatuhu, Shaykh. Is it true that it is from the Sunnah of Prophet Muhammad, sallallaahu ‘alayhi wa sallam, to say, 'Alhamdulillaahi Rabbil-‘Aalameen' after reciting the last verse of Surah Al-Mulk or after reciting Surah Al-Mulk? May Allaah reward you, Shaykh.
All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
We did not find any scholar stating that it is an act of the Sunnah to say 'Alhamdulillahi Rabbil-‘Aalameen' after reciting the last verse of Soorah Al-Mulk (Quran 67).
The Shaafi‘i scholar Al-Khateeb Ash-Shirbeeni wrote:
"It is an act of the Sunnah for the person reciting the Quran inside or outside the prayer to contemplate the verses being recited, seek the mercy of Allah when reading a verse in which mercy is mentioned, seek refuge in Allah from His punishment when reciting a verse on punishment, glorify Allah when His Glorification is mentioned in a verse, reflect on a verse urging him to contemplate, and so forth. When he recites (the last verse of Soorah At-Teen): {Is not Allah the most just of judges?} [Quran 95:8], he may say, 'Certainly, and I am one of those who testify to that.' When he recites (the last verse of Soorah Al-Mursalaat): {Then in what statement after the Quran will they believe?} [Quran 77:50], he may say, 'I believe in Allah.' And when he recites (the last verse of Soorah Al-Mulk): {Then who could bring you flowing water?} [Quran 67:30], he may say, 'Allah Rabbul-‘Aalameen (Allah, the Lord of the worlds)." [Mughni Al-Muhtaaj]
As far as we know, no hadeeth has been reported about this verse in particular.
Shaykh Ibn ‘Uthaymeen wrote:
"When the person recites: {Say: Have you considered: if your water was to become sunken (into the earth), then who could bring you flowing water?} [Quran 67:30], he should not say, 'Allah will bring it.' This is because the context of the verse is a warning and a threat of punishment for the disbelievers. Allah, The Exalted, commanded the Prophet, sallallahu ‘alayhi wa sallam, to say tho them (what means): {Have you considered: if your water was to become sunken (into the earth), then who could bring you flowing water?} [Quran 67:30] And we hear the laymen say, 'Allah will bring it,' and this is wrong." [Ash-Sharh Al-Mumti‘]
Allah knows best.
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