Ali said, "It is part of the Sunnah to place one hand over the other in prayer below the navel."
حدثنا محمد بن محبوب حدثنا حفص بن غياث عن عبد الرحمن بن إسحق عن زياد بن زيد
أن عليا رضي الله عنه قال من السنة وضع الكف على الكف في الصلاة تحت السرة
Its chain is daif. Abdullah bin Ahmad reported it in Zawaid al-Musnad (1/110) from the hadith of Abdul-Rahman bin Ishaq Kufi through this route, and he is daif, the majority having declared him daif, while Ziyad bin Zayd is unknown (see Taqrib).