Hisham bin Ishaq bin Abdullah narrates that his father said: One of the governors sent me to Ibn Abbas (may Allah be pleased with them both) to ask him about the rain prayer (salat al-istisqa'). Ibn Abbas (may Allah be pleased with them both) said: Who sent you? I said: So-and-so. He said: What prevented him from coming to me and asking me? Then Ibn Abbas (may Allah be pleased with them both) said: He (peace and blessings be upon him) went out humbly and imploring, and he (peace and blessings be upon him) did not deliver a sermon like this sermon of yours, and he led two rak'ahs just as he used to lead them at Eid.
Sufyan (may Allah have mercy on him) said: I said to the Shaykh: Was the sermon before the two rak'ahs or after them? He said: I do not know. This indicates that Hisham had not retained it, and Isma'il bin Rabi'ah bin Hisham narrated it from his grandfather, referring it to the prayer of the two Eids.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الاستسقاء / 6403