Narrated by Sahel Ibn Sa’ad (radiallaahu anhu), that the Messenger of Allah (sallallaahu alaihi wasallam) said,
“Two will not be rejected, Supplication when the Adhan (call of prayer) is being called, and at the time of the rain”

Narrated Anas bin Malik (Radiyallaahu `anhu),
“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)”.