Abu Dawud said: I heard Ahmad b. Hanbal say: The narrator 'Abd al-Rahman b. Ishaq al-Kufi is weak (i.e. not reliable).
In-book : Book 2, Hadith 368
English translation : Book 3, Hadith 757
2. Prayer (Kitab Al-Salat)
باب وَضْعِ الْيُمْنَى عَلَى الْيُسْرَى فِي الصَّلاَةِ