Narrated Aisha, Ummul Mu'minin (mother of the believers): When the Prophet (ﷺ) saw a cloud formation in the sky, he would stop what he was doing, even if he were in prayer, and then would say: "O Allah! I seek refuge in You from its evil. "If it rained, he would say: "O Allah! send a beneficial downpour."
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا ابْنُ بَشَّارٍ، حَدَّثَنَا عَبْدُ الرَّحْمَنِ، حَدَّثَنَا سُفْيَانُ، عَنِ الْمِقْدَامِ بْنِ شُرَيْحٍ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، رَضِيَ اللَّهُ عَنْهَا أَنَّ النَّبِيَّ صلى الله عليه وسلم كَانَ إِذَا رَأَى نَاشِئًا فِي أُفُقِ السَّمَاءِ تَرَكَ الْعَمَلَ وَإِنْ كَانَ فِي صَلاَةٍ ثُمَّ يَقُولُ " اللَّهُمَّ إِنِّي أَعُوذُ بِكَ مِنْ شَرِّهَا " . فَإِنْ مُطِرَ قَالَ " اللَّهُمَّ صَيِّبًا هَنِيئًا " .
sunnah.com