Sahih al-Bukhari 4583Book 65, Hadith 105
حَدَّثَنَا مُحَمَّدٌ، أَخْبَرَنَا عَبْدَةُ، عَنْ هِشَامٍ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ ـ رضى الله عنها ـ قَالَتْ هَلَكَتْ قِلاَدَةٌ لأَسْمَاءَ فَبَعَثَ النَّبِيُّ صلى الله عليه وسلم فِي طَلَبِهَا، رِجَالاً فَحَضَرَتِ الصَّلاَةُ وَلَيْسُوا عَلَى وُضُوءٍ. وَلَمْ يَجِدُوا مَاءً، فَصَلَّوْا وَهُمْ عَلَى غَيْرِ وُضُوءٍ، فَأَنْزَلَ اللَّهُ. يَعْنِي آيَةَ التَّيَمُّمِ.
The necklace of Asma' was lost, so the Prophet (ﷺ) sent some men to look for it. The time for the prayer became due and they had not performed ablution and could not find water, so they offered the prayer without ablution. Then Allah revealed (the Verse of Tayammum).