اللَّهُمَّ صَيِّبًا نَافِعًا
Allahumma sayyiban nafi'a
O Allah, let it be a beneficial rain.
The Prophet ﷺ would say this when he saw rain. Rain is a time when du'as are answered — the Prophet ﷺ said: "Two du'as are not rejected: the du'a at the time of the adhan, and the du'a at the time of rain."
Related Du'as
اللَّهُمَّ اسْقِنَا اللَّهُمَّ اسْقِنَا اللَّهُمَّ اسْقِنَا
O Allah, give us rain. O Allah, give us rain. O Allah, give us rain.
Sahihاللَّهُمَّ اغْفِرْ لِي
O Allah, forgive me. (Du'a during rainfall is accepted.)
Hasanاللَّهُمَّ اسْقِنَا غَيْثًا مُغِيثًا مَرِيئًا مَرِيعًا نَافِعًا غَيْرَ ضَارٍّ عَاجِلًا غَيْرَ آجِلٍ
O Allah, send us rain that is helpful, productive, wholesome, beneficial and not harmful, soon and not delayed.
Sahihاللَّهُمَّ إِنِّي أَسْأَلُكَ مِنْ خَيْرِ مَا سَأَلَكَ عَبْدُكَ وَنَبِيُّكَ مُحَمَّدٌ وَأَعُوذُ بِكَ مِنْ شَرِّ مَا اسْتَعَاذَ مِنْهُ عَبْدُكَ وَنَبِيُّكَ
O Allah, I ask You for the good that Your servant and Prophet Muhammad ﷺ asked You for, and I seek refuge in You from the evil that Your servant and Prophet sought refuge from.
Hasan