(122) باب وَضْعِ الْيُمْنَى عَلَى الْيُسْرَى فِي الصَّلاَةِ
Narrated Ali ibn AbuTalib:
AbuJuhayfah said: Ali said that it is a sunnah to place one hand on the other in prayer below the navel.
Reference: Sunan Abi Dawud 756
In-book reference: Book 2, Hadith 366
English translation: Book 3, Hadith 755