Raise both hands and should recite,

ااَللّهُمَّ اسْقِنَا اَللّهُمَّ اسْقِنَا اَللّهُمَّ اسْقِنَا

Allâhumma askinâ ! Allâhumma askinâ ! Allâhumma askinâ !

Meaning:
O Allah! Give us rain. O Allah! Give us rain. O Allah! Give us rain!
(Book: Bukhari 1013)

OR

اَللّهُمَّ أَغِثْنَا اَللّهُمَّ أَغِثْنَا اَللّهُمَّ أَغِثْنَا

Allâhumma aghithnâ ! Allâhumma aghithnâ ! Allâhumma aghithnâ !

Meaning:
O Allah! Bless us with rain. O Allah! Bless us with rain. O Allah! Bless us with rain!
(Book: Bukhari 1014)