When it rained the Messenger of Allah would say: "Allahummaj'alhu Sayyiban nafiʿa. (O Allah, make it beneficial rain)."  

أَنَّ رَسُولَ اللَّهِ ﷺ كَانَ إِذَا أُمْطِرَ قَالَ اللَّهُمَّ اجْعَلْهُ صَيِّبًا نَافِعًا