It is narrated from Hazrat Abu Saeed Khudri (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) was standing in the plain of Arafat making supplication in such a manner that the backs of his hands were facing the ground.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 11803
Hadith Gradingحکم دارالسلام:إسناده ضعيف لضعف بشر بن حرب الأزدي