Ayesha reported,

Ayesha reported that whenever it was a windy or cloudy day, the effect of it would show on the face of the Messenger of Allah ﷺ. He would pace back and forth restlessly. But once the rain fell, he would be relieved and the unease would leave him.Ayesha said, "I asked him about this, and he replied, 'I feared it might be a punishment sent upon my nation.'" And whenever he saw the rain, he would say, "Mercy."

Azami 11084

Sahih

عن عائشة زوج النبي ﷺ

قالت: كان رسول الله ﷺ إذا كان يوم الريح والغيم، عرف ذلك في وجهه، وأقبل وأدبر، فإذا مطرت سر به وذهب عنه ذلك. قالت عائشة: فسألته فقال: إني خشيت أن يكون عذابا سلط على أمتي. ويقول إذا رأى المطر: رحمة.

الأعظمي 11084صحيح
Contents
Reference
Commentary
Ayat
Collection
Jami al-Kamil
Book
Supplications, remembrances, and prayer upon the chosen Prophet ﷺ
Chapter
Supplications of adhan and prayer, and what is related to them
Section
What to say when one sees rain
Numbering
Jami al-Kamil 11084 (2nd edition)
Azami 11084