The one who knows everything in the heavens and on earth, and knows the number of drops of water and the number of grains of sand is Allah, the Lord of the Worlds. There is no angel who is close to Him or any Prophet who was sent who has this knowledge. Anyone who says that there is anyone among the angels who knows all of this has fabricated a lie against Allah, to Whom belongs knowledge of the unseen of the heavens and the earth.
Allah, may He be exalted, says (interpretation of the meaning):
“And with Him are the keys of the Ghaib (all that is hidden), none knows them but He. And He knows whatever there is in (or on) the earth and in the sea; not a leaf falls, but he knows it. There is not a grain in the darkness of the earth nor anything fresh or dry, but is written in a Clear Record” [6:59].
And He, may He be glorified, says (interpretation of the meaning):
“Say: None in the heavens and the earth knows the Ghaib (unseen) except Allah, nor can they perceive when they shall be resurrected” [27:65].
Ibn Katheer (may Allah have mercy on him) said: Here Allah, may He be exalted, is instructing His Messenger (blessings and peace of Allah be upon him) to tell all of mankind that no one knows the unseen except Allah, may He be glorified and exalted, and that He alone has that knowledge, with no partner or associate. End quote from Tafseer Ibn Katheer, (6/207).
Al-Bukhaari (4697) narrated from Ibn ‘Umar (may Allah be pleased with him) that the Messenger of Allah (blessings and peace of Allah be upon him) said: “The keys of the Unknown are five, which no one knows except Allah: no one knows what will happen tomorrow except Allah; no one knows what is in the wombs except Allah; no one knows when it will rain except Allah; no one knows in which land he will die; and no one knows when the Hour will begin except Allah.”
But Allah, may He be exalted, may inform whomever He wills among His creation about whatever He wills of His unseen. Allah, may He be exalted, says (interpretation of the meaning):
“(He Alone) the All-Knower of the Ghaib (unseen), and He reveals to none His Ghaib (unseen). Except to a Messenger (from mankind) whom He has chosen (He informs him of the unseen as much as He likes), and then He makes a band of watching guards (angels) to march before him and behind him.” [72:26, 27].
The scholars of the Standing Committee said: Knowledge of unseen matters is something that belongs exclusively to Allah, so no one among His creation, human or jinn, knows anything of it except what Allah reveals to whomever He wills among His Angels or His Messengers. End quote from Fataawa al-Lajnah ad-Daa’imah, (1/346).
Yes, there is an angel who is appointed in charge of the rain, and directs it wherever Allah wills; he is Mikaa’eel (peace be upon him), who has helpers who do whatever he instructs them to do. But this only happens by the will of Allah and in accordance with His wisdom and knowledge. They do not know anything or do anything; rather they cannot do anything at all except by Allah’s leave. Moreover, that does not mean that they know the number of drops of water, because their knowledge is restricted to what Allah has taught them, and they say, as Allah tells us:
“Glory be to You, we have no knowledge except what you have taught us. Verily, it is You, the All-Knower, the All-Wise”
And Allah knows best.