سنن أبي داود

Narrated 'Aishah:

The revelation came down to Messenger of Allah (ﷺ) and he recited to is: "A surah which We have sent down and which We have ordained (faradnaha)"

Abu Dawud said: The letter ra (r) is the word faradnaha has short vowel a (with out doubling of consonant r), and then he reached the verses after this verse.