At the time of seeking rain, one should recite the following dua
اللّٰهُمَّ اسْقِنَا، اللّٰهُمَّ اسْقِنَا، اللّٰهُمَّ اسْقِنَا
O Allah, Bless us with rain! O Allah, Bless us with rain! O Allah, Bless us with rain!
عن أنس بن مالك أن رجلا دخل يوم الجمعة من باب كان وجاه المنبر، ورسول الله صلى الله عليه وسلم قائم يخطب، فاستقبل رسول الله صلى الله عليه وسلم قائما، فقال: يا رسول الله: هلكت المواشي، وانقطعت السبل، فادع الله يغيثنا، قال: فرفع رسول الله صلى الله عليه وسلم يديه، فقال: اللهم اسقنا، اللهم اسقنا، اللهم اسقنا قال أنس: ولا والله ما نرى في السماء من سحاب، ولا قزعة ولا شيئا وما بيننا وبين سلع من بيت، ولا دار قال: فطلعت من ورائه سحابة مثل الترس، فلما توسطت السماء، انتشرت ثم أمطرت. (صحيح البخاري، الرقم: 1014)
Hazrat Anas (radhiyallahu ‘anhu) reports that once a person entered the musjid on the day of Jumuah from the door which was in the direction of the mimbar. He entered while Rasulullah (sallallahu ‘alaihi wasallam) was delivering the Khutbah. The man stood in front of Rasulullah (sallallahu ‘alaihi wasallam) and said, “O Rasulullah (sallallahu ‘alaihi wasallam)! The livestock are dying and the roads are cut off (due to the animals being too weak for travel); so make dua to Allah Ta‘ala for rain.” Rasulullah (sallallahu ‘alaihi wasallam) raised both his hands and made dua saying:
اللّٰهُمَّ اسْقِنَا، اللّٰهُمَّ اسْقِنَا، اللّٰهُمَّ اسْقِنَا
Hazrat Anas (radhiyallahu ‘anhu) further says, “By Allah, we could not see any cloud in the sky nor any sign of rain, and there was no house or dwelling between us and (the mountains of) Sala’. Then a cloud (round in shape) like a shield appeared from behind it (i.e. the Sala’ Mountain). When it came in the middle of the sky, it spread out (and grew until it covered the entire sky) and then it began to rain.”