The prophet ﷺ did not distinguish between the two surahs until the words “In the name of Allah, the Compassionate, the merciful” was revealed to him. These are the words of Ibn al-sarh.

كَانَ النَّبِيُّ ﷺ لاَ يَعْرِفُ فَصْلَ السُّورَةِ حَتَّى تُنَزَّلَ عَلَيْهِ { بِسْمِ اللَّهِ الرَّحْمَنِ الرَّحِيمِ } وَهَذَا لَفْظُ ابْنِ السَّرْحِ

"The Prophet would open his Salat with (Bismillahir-Rahmanir-Rahim)."

كَانَ النَّبِيُّ ﷺ يَفْتَتِحُ صَلاَتَهُ بِ (بِسْمِ اللَّهِ الرَّحْمَنِ الرَّحِيمِ )

[AI] The recitation of the Prophet ﷺ of "In the name of Allah, the Most Gracious, the Most Merciful" [Surah Al-Fatiha, verse 1] was letter by letter, in a slow recitation that Abdullah ibn Mas'ud considered to be prolonged.

أَنَّ قِرَاءَةَ النَّبِيِّ ﷺ كَانَتْ فَوَصَفَ {بِسْمِ اللهِ الرَّحْمَنِ الرَّحِيمِ} [الفاتحة 1] حَرْفًا حَرْفًا قِرَاءَةً بَطِيئَةً قَطَّعَ عَفَّانُ قِرَاءَتَهُ

[AI] The Prophet ﷺ used to recognize that it was a Surah when Gabriel came to him and recited "Bismillah ar-Rahman ar-Rahim"

أَنَّ النَّبِيَّ ﷺ كَانَ «إِذَا جَاءَهُ جِبْرِيلُ فَقَرَأَ بِسْمِ اللَّهِ الرَّحْمَنِ الرَّحِيمِ عَلِمَ أَنَّهَا سُورَةٌ»

[AI] Indeed, the Prophet ﷺ used to say "Bismillah ar-Rahman ar-Rahim" (In the name of Allah, the Most Gracious, the Most Merciful) when Jibril (Gabriel) ﷺ revealed to him a surah.

إِنَّ النَّبِيَّ ﷺ كَانَ إِذَا نَزَلَ جِبْرِيلُ عَلَيْهِ السَّلَامُ فَقَالَ بِسْمِ اللَّهِ الرَّحْمَنِ الرَّحِيمِ عَلِمَ أَنَّهَا سُورَةٌ

[AI] The Prophet ﷺ used to say aloud "Bismillah Ar-Rahman Ar-Rahim" (In the name of Allah, the Most Gracious, the Most Merciful).

أَنَّ النَّبِيَّ ﷺ «كَانَ يَجْهَرُ بِبِسْمِ اللهِ الرَّحْمَنِ الرَّحِيمِ»

[AI] The Messenger of Allah ﷺ did not know the ending of the Surah until "In the name of Allah, the Most Gracious, the Most Merciful" was revealed to him.

«مَا كَانَ رَسُولُ اللهِ ﷺ يَعْرِفُ خَاتِمَةَ السُّورَةِ حَتَّى يُنَزَّلَ عَلَيْهِ بِسْمِ اللهِ الرَّحْمَنِ الرَّحِيمِ»

[AI] Gabriel, ﷺ , used to descend upon the Messenger of Allah, ﷺ , revealing to him the divine revelation. And when he said, "In the name of Allah, the Most Gracious, the Most Merciful," he began another chapter.

كَانَ جِبْرِيلُ عَلَيْهِ السَّلَامُ يُنَزِّلُ عَلَى رَسُولِ اللهِ ﷺ الْوَحْيَ فَإِذَا قَالَ بِسْمِ اللهِ الرَّحْمَنِ الرَّحِيمِ افْتَتَحَ سُورَةً أُخْرَى

[AI] The Messenger of Allah ﷺ would not know the division of the surah (chapter) until "Bismillah Al-Rahman Al-Raheem" (In the name of Allah, the Most Gracious, the Most Merciful) would be revealed to him.

كَانَ رَسُولُ اللهِ ﷺ لَا يَعْرِفُ فَصْلَ السُّورَةِ حَتَّى تَنْزِلَ عَلَيْهِ بِسْمِ اللهِ الرَّحْمَنِ الرَّحِيمِ

"The Prophet would open his Salat with (Bismillahir-Rahmanir-Rahim)." (Using translation from Tirmidhī 245)

كَانَ يَفْتَتِحُ الصَّلَاةَ بِ {بِسْمِ اللهِ الرَّحْمَنِ الرَّحِيمِ} [الفاتحة 1]

[AI] He used to say that the reading begins with "In the name of Allah, the Most Gracious, the Most Merciful" [Surah Al-Fatiha 1].

كَانَ يَقُولُ تُفْتَتَحُ الْقِرَاءَةُ بِ {بِسْمِ اللهِ الرَّحْمَنِ الرَّحِيمِ} [الفاتحة 1]

[AI] In the name of Allah, the Most Gracious, the Most Merciful. When he finishes reciting the opening chapter of the book, he says that when he begins reciting the surah.

بِسْمِ اللهِ الرَّحْمَنِ الرَّحِيمِ فَإِذَا فَرَغَ مِنْ فَاتِحَةِ الْكِتَابِ قَالَ ذَلِكَ حِينَ يَسْتَفْتِحُ السُّورَةَ

" بِسم اللهِ الرحمنِ الرحيمِ مِفتاحُ كلِّ كِتَابِ".

"عَن عَلِىٍّ قال: كانَ رسُولُ الله ﷺ يَقْرَأُ بِسم الله الرَّحمن الرَّحِيم في صَلاَته".

"عَنِ ابْنِ عُمَرَ أنَّ النَّبىَّ ﷺ كَانَ يَفْتَتِحُ الْقِرَاءَةَ بِبِسْم الله الرَّحْمنِ الرَّحِيمِ".