“Two will not be rejected, Supplication when the Adhan (call of prayer) is being called, and at the time of the rain”

Al-Hakim 2: 114, and Abu Dawud #2540, ibn Majah

In another hadith,

“When the prayer is called, the doors of the skies are opened, and the du’a is answered”

al-Tayalisi in his Musnad #2106, al-Sahihah #1413

“…the dua of a muslim for his brother (in Islam) in his absence is readily accepted, and an angel is appointed to his side, whenever he makes a beneficial dua for his brother the appointed angel says “Ameen and may you also be blessed with the same.”

Muslim

“If any one of you says, ‘Ameen’ and the angels in the heavens say ‘Ameen’ and the former coincides with the latter, all his past sins will be forgiven.”

Sahih Al-Bukhari Vol. 1 : No. 748

“Once in the lifetime of the Prophet (p.b.u.h) the people were afflicted with drought (famine). While the Prophet was delivering the Khutba on a Friday, a Bedouin stood up and said, “O, Allah’s Apostle! Our possessions are being destroyed and the children are hungry; Please invoke Allah (for rain)”.

So the Prophet raised his hands. At that time there was not a trace of cloud in the sky. By Him in Whose Hands my soul is as soon as he lowered his hands, clouds gathered like mountains, and before he got down from the pulpit, I saw the rain falling on the beard of the Prophet.

It rained that day, the next day, the third day, the fourth day till the next Friday.

The same Bedouin or another man stood up and said, “O Allah’s Apostle! The houses have collapsed, our possessions and livestock have been drowned; Please invoke Allah (to protect us)”. So the Prophet I raised both his hands and said, “O Allah! Round about us and not on us”. So, in whatever direction he pointed with his hands, the clouds dispersed and cleared away, and Medina’s (sky) became clear as a hole in between the clouds.

The valley of Qanat remained flooded, for one month, none came from outside but talked about the abundant rain.”

Sahih Bukhari. Volume 2, Book 13, Number 55.

“No one offers a supplication without Allah bringing him what he asks or keeping away from him a like amount of evil, provided he does not ask for something sinful or for breaking ties of relationship.”

Tirmidhi, Narrated Jabir ibn Abdullah