Abbad bin Tamim narrates from his uncle (may Allah be pleased with him) that he (peace and blessings be upon him) went out for the rain prayer, and he said: He (peace and blessings be upon him) turned his cloak around, placing its right side on his left shoulder and its left side on his right shoulder; then he supplicated to Allah Almighty.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الاستسقاء / 6415
Abbad bin Tamim reports from his uncle Abdullah bin Zayd (may Allah be pleased with him) that he said: The Messenger of Allah (peace and blessings be upon him) went out to the prayer ground seeking rain. He (peace and blessings be upon him) turned his cloak around, faced the qiblah, and prayed two rak'ahs.
Al-Mas'udi said: I said to Abu Bakr: Did he (peace and blessings be upon him) put the right side on the left and the left on the right, or did he put the upper part at the bottom? He said: Rather, he put the right side on the left and the left side on the right.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الاستسقاء / 6416
Sayyiduna Abdullah bin Zayd (may Allah be pleased with him) says that the Prophet (peace and blessings be upon him) supplicated for rain while he (peace and blessings be upon him) was wearing a black garment. He (peace and blessings be upon him) intended to take hold of its lower part and put it on top, but when he (peace and blessings be upon him) grew tired he placed it over his neck. The wording of both (narrations) is the same.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الاستسقاء / 6417