WE RELATE FROM the Ṣaḥīḥ of al-Bukhārī from ‘Ā’ishah 
who reported that when the Messenger of Allah 
saw rain he would say: “O Allah, make it beneficial rain.” [1].
who reported that when the Messenger of Allah saw rain he would say: “O Allah, make it beneficial rain.” [1].
Allāhumma ṣayyiban nāfi‘ā.
We relate it in the Sunan of Ibn Mājah in which he said:
Allāhumma sayban nāfi‘ā.
twice or thrice.
Ash-Shāfi‘ī reports in al-Umm that the Messenger of Allah said: “Look for the acceptance of du‘ā’ when armies meet, when the iqāmah is called for ṣalāh, and when it rains.” Ash-Shāfi‘ī said: “I learned from more than one person to look for the acceptance of supplications when the iqāmah is called for ṣalāh and when rain falls.” [2].
said: “Look for the acceptance of du‘ā’ when armies meet, when the iqāmah is called for ṣalāh, and when it rains.” Ash-Shāfi‘ī said: “I learned from more than one person to look for the acceptance of supplications when the iqāmah is called for ṣalāh and when rain falls.” [2].References
[1] Al-Bukhārī (1032) and Ibn Mājah (3890).
[2] Al-Umm (1/223–224).