Sahih Bukhari Volume 6, Book 61, Hadith Number 566.

Narrated By 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.