Musannaf Ibn Abi Shayba 3:5960

Waki' narrated to us, he said: Yunus bin Abi Ishaq narrated to us, from his father, from Harithah bin Mudharrib al-'Abdi, he said: We went out with Abu Musa to pray for rain, so he led us in two rak'ahs without an adhan and without an iqamah.