Narrated Qatada:

Anas was asked, "How was the recitation (of the Quran) of the Prophet?' He replied, "It was characterized by the prolongation of certain sounds." He then recited: In the Name of Allah, the Most Beneficent, the Most Merciful prolonging the pronunciation of 'In the Name of Allah, 'the most Beneficent,' and 'the Most Merciful.

حَدَّثَنَا عَمْرُو بْنُ عَاصِمٍ، حَدَّثَنَا هَمَّامٌ، عَنْ قَتَادَةَ، قَالَ سُئِلَ أَنَسٌ كَيْفَ كَانَتْ قِرَاءَةُ النَّبِيِّ ﷺ. فَقَالَ كَانَتْ مَدًّا. ثُمَّ قَرَأَ بِسْمِ اللَّهِ الرَّحْمَنِ الرَّحِيمِ، يَمُدُّ بِبِسْمِ اللَّهِ، وَيَمُدُّ بِالرَّحْمَنِ، وَيَمُدُّ بِالرَّحِيمِ.