Musannaf Ibn Abi Shayba 35:383

Shababa ibn Sawwar narrated to us, from Ibn Abi Dhi'b, from al-Zuhri, from 'Abbad ibn Tamim, from 'Abdullah ibn Zayd—and he was one of the companions of the Prophet, may Allah bless him and grant him peace—that he saw the Prophet, may Allah bless him and grant him peace, on the day he went out to pray for rain. He turned his back to the people while supplicating and faced the Qibla. Then he turned his cloak, then he prayed two rak'ahs and recited in them aloud. And he mentioned that Abu Hanifa said: The prayer for rain is not to be performed in congregation, and there is no sermon in it.