What is the intended meaning of the transmitted supplication said upon rainfall, “O Allah, [grant us] beneficial rain?”

It has been reported on the authority of the Mother of the Believers, Lady ʿAisha (may Allah be pleased with her), that whenever the Messenger of Allah (peace and blessings be upon him and his family) saw rain, he would say, “O Allah, [grant us] beneficial rain” (Allahumma sayyiban nafiʿan). This was narrated by al-Bukhari in his Sahih. In another wording reported by Abu Dawud in his Sunan, he would say, “O Allah, [grant us] pleasant rain” (Allahumma sayyiban haniʾan).

There are also other supplications reported to be said in this circumstance. Among them:
On the authority of Anas (may Allah be pleased with him), the Prophet (peace and blessings be upon him and his family) said, “O Allah, [let the rain fall] around us and not upon us. O Allah, [let it fall] upon the hilltops, the mountains, the thickets, the valleys, and the places where trees grow” (recorded by Bukhari and Muslim).

And on the authority of Jabir ibn ʿAbduallah (may Allah be pleased with them both), who said, “I saw the Messenger of Allah (peace and blessings be upon him and his family) supplicating, ‘O Allah, give us rain that brings relief, nourishing, wholesome, beneficial and not harmful, immediate and not delayed’” (reported by Abu Dawud in his Sunan).

From the overall purport of these prophetic narrations, it is understood that it is recommended to supplicate upon rainfall. A person should ask his Lord to make it rain that is beneficial for people and lands, and not rain of punishment, destruction, or flooding—such as the devastating torrents by which Allah destroyed the people of Prophet Nuh (peace be upon him).[1]

On the authority of ʿAisha (may Allah be pleased with her), in a marfuʿ narration, “Whenever the Prophet (peace and blessings be upon him) saw rain, he would say, ‘O Allah, [grant us] beneficial rain’ (reported by Ahmad and Bukhari).”

And Allah Almighty knows best.