Sunan an Nasai 1523
The Book of Praying for Rain (Al-Istisqa')
أَخْبَرَنَا مُحَمَّدُ بْنُ مَنْصُورٍ، قَالَ حَدَّثَنَا سُفْيَانُ، عَنْ مِسْعَرٍ، عَنِ الْمِقْدَامِ بْنِ شُرَيْحٍ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ إِذَا أُمْطِرَ قَالَ " اللَّهُمَّ اجْعَلْهُ صَيِّبًا نَافِعًا " .
It was narrated from 'Aishah that:When it rained the Messenger of Allah would say: "Allahummaj'alhu Sayyiban nafi`a. (O Allah, make it beneficial rain)
Grading: Abu Ghuddah: Sahih · Al-Albani: Sahih · Zubair Ali Zai: Isnaad Sahih
Text from the public-domain hadith-api dataset. Numbering follows that dataset and can differ by a few from some printed editions — check the wording, not only the number.