Anas ibn Malik reported: The Prophet, peace and blessings be upon him, would perform ablution at the time of every prayer. ‘Amr said, “How would you do so?” Anas said, “It is permissible for one of us to maintain ablution for multiple prayers, as long as he does not become ritually impure.”
Source: Ṣaḥīḥ al-Bukhārī 248
Grade: Sahih (authentic) according to Al-Bukhari
عَنْ أَنَسِ بْنِ مَالِكٍ قَالَ كَانَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَتَوَضَّأُ عِنْدَ كُلِّ صَلَاةٍ قال عمرو كَيْفَ كُنْتُمْ تَصْنَعُونَ قَالَ يُجْزِئُ أَحَدَنَا الْوُضُوءُ مَا لَمْ يُحْدِثْ
248 صحيح البخاري كتاب الوضوء باب الوضوء من غير حدث