Ishaq bin Ibrahim says that Waki' explained, regarding his words that he (peace and blessings be upon him) put the right side of the cloak onto the left and the left side onto the right: that is, (it is a hope) that He turns drought into greenery, just as the cloak has been turned from the right side to the left side.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الاستسقاء / 6420