It is narrated from Abbad bin Tamim (may Allah have mercy on him) that his uncle, who was one of the Companions of the Prophet (peace and blessings be upon him) (may Allah be pleased with them), informed Abbad that the Prophet (peace and blessings be upon him) went out with the people to the prayer ground to ask for rain for them. He (peace and blessings be upon him) stood up and supplicated while standing. Then he (peace and blessings be upon him) turned towards the qiblah and turned his cloak around, and they were given rain.
Abu al-Yaman (may Allah have mercy on him) also narrated the hadith in the same way; he said: then he supplicated standing, and he said: then they were given rain. Imam Bukhari (may Allah have mercy on him) narrated it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الاستسقاء / 6411