Musannaf Ibn Abi Shayba 21:103

Yazid ibn al-Miqdam ibn Shurayh narrated to us, from his father al-Miqdam, from his father, that he mentioned from Aisha, that she narrated to him that the Messenger of Allah (peace and blessings of Allah be upon him), when he saw a cloud approaching from any of the horizons, would leave what he was doing—even if he were in his prayer—until he faced it. Then he would say: "O Allah, we seek refuge in You from the evil of what it has been sent with." If it rained, he would say: "O Allah, a beneficial downpour," twice or three times. If Allah cleared it away and it did not rain, he would praise Allah for that.