At the time of seeking rain, one should recite the following dua:
اللّٰهُمَّ أَنْزِلْ فِي أَرْضِنَا زِينَتَهَا وَسَكَنَهَا
O Allah, send down such rain in our land which will be the cause of beauty and tranquility coming about (i.e. such rain which will be the cause of beauty and adornment through it greenery and beautiful growth and a means of tranquility for the people by them seeing the vegetation growth and good harvest)
عن سمرة، أن النبي صلى الله عليه وسلم كان إذا استسقى قال: اللهم أنزل في أرضنا زينتها وسكنها (المعجم الكبير للطبراني، الرقم: 6904)
Hazrat Samurah (radhiyallahu ‘anhu) reports that Rasulullah (sallallahu ‘alaihi wasallam) would recite the following dua when seeking rain:
اللّٰهُمَّ أَنْزِلْ فِي أَرْضِنَا زِينَتَهَا وَسَكَنَهَا