Hadith 504570
Chapter 13: Asking for Rain - كتاب الاستسقاء
وَحَدَّثَنِي عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ أَبَا هُرَيْرَةَ، كَانَ يَقُولُ إِذَا أَصْبَحَ وَقَدْ مُطِرَ النَّاسُ مُطِرْنَا بِنَوْءِ الْفَتْحِ ثُمَّ يَتْلُو هَذِهِ الآيَةَ {مَا يَفْتَحِ اللَّهُ لِلنَّاسِ مِنْ رَحْمَةٍ فَلاَ مُمْسِكَ لَهَا وَمَا يُمْسِكْ فَلاَ مُرْسِلَ لَهُ مِنْ بَعْدِهِ }
Yahya related to me from Malik that he had heard that Abu Hurayra used to say, when morning came after it had rained on the people, "We have been rained upon by the rain of Allah's opening," and would then recite the ayat, "Whatever Allah opens to man of His mercy no-one can withhold, and whatever He withholds no-one can send forward after Him. " (Sura 35 ayat 2).
Reference Muwatta Malik 504570
USC-MSA web (English) reference : Book 13, Hadith 6