Mishkat al-Masabih 4 Prayer كتاب الصلاة 913

وَعَنِ ابْنِ عُمَرَ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ ” مَفَاتِيحُ الْغَيْبِ خَمْسٌ ثُمَّ قَرَأَ: (إِنَّ اللَّهَ عِنْدَهُ عِلْمُ السَّاعَةِ وَيُنَزِّلُ الْغَيْثَ) الْآيَة. رَوَاهُ البُخَارِيّ

Ibn ‘Umar reported God’s Messenger as saying, “The keys of the unseen are five.” He then recited, “God has knowledge of the Hour, and He sends down the rain . . .” (Al-Qur’an; 31:34). Bukhari transmitted it.