Sahih al-Bukhari 5046
Narrated Qatada:
Anas was asked, "How was the recitation (of the Qur'an) 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 صلى الله عليه وسلم‏.‏ فَقَالَ كَانَتْ مَدًّا‏.‏ ثُمَّ قَرَأَ بِسْمِ اللَّهِ الرَّحْمَنِ الرَّحِيمِ، يَمُدُّ بِبِسْمِ اللَّهِ، وَيَمُدُّ بِالرَّحْمَنِ، وَيَمُدُّ بِالرَّحِيمِ‏.‏