Qatada reported,

Anas was asked how the Prophet ﷺ used to recite. He replied, "He would draw out the letters." Then he recited "In the name of Allah, the Most Gracious, the Most Merciful" [Fatihah 1:1], drawing out "In the name of Allah," drawing out "the Most Gracious," and drawing out "the Most Merciful."

Azami 13629

Sahih

عن قتادة قال

سئل أنس كيف كانت قراءة النبي ﷺ؟ فقال: كانت مدا مدا، ثم قرأ {بسم الله الرحمن الرحيم} يمد {بسم الله} ويمد {الرحمن} ويمد {الرحيم}

الأعظمي 13629صحيح
Contents
Reference
Commentary
Ayat
Collection
Jami al-Kamil
Book
Tafsir of the great Quran
Chapter
Tafsir of Surah Muzzammil
Section
His saying, "O you wrapped in garments, stand in prayer at night except for a little, half of it or subtract from it a little, or add to it and recite the Quran with measured recitation"
Numbering
Jami al-Kamil 13629 (2nd edition)