It was narrated that Abu Ghutaif Al-Hudhali said:
"I was listening to 'Abdullah bin 'Umar bin Khattab in the mosque, and when the time for prayer came, he got up, performed ablution, and offered prayer, then he went back to where he had been sitting. When the time for 'Asr (Afternnon prayer) came, he got up, performed ablution, and offered prayer, then he went back to where he had been sitting. When the time for Maghrib (Sunset prayer) came, he got up, performed ablution, and offered prayer, then he went back to where he had been sitting. I said: 'May Allah improve you (i.e., your condition) Is it obligatory or Sunnah to perform ablution for every prayer?' He said: 'Did you notice that?' I said: 'Yes.' He said: 'No (it is not obligatory). If I perform ablution for Morning prayer I can perform all of the prayers with this ablution, so as long as I do not get impure. But I heard the Messenger of Allah say: "Whoever performs ablution while he is pure, he will have ten merits." So I wanted to earn the merits.'"

حَدَّثَنَا مُحَمَّدُ بْنُ يَحْيَى، حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يَزِيدَ الْمُقْرِئُ، حَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ زِيَادٍ، عَنْ أَبِي غُطَيْفٍ الْهُذَلِيِّ، قَالَ سَمِعْتُ عَبْدَ اللَّهِ بْنَ عُمَرَ بْنِ الْخَطَّابِ، فِي مَجْلِسِهِ فِي الْمَسْجِدِ فَلَمَّا حَضَرَتِ الصَّلاَةُ قَامَ فَتَوَضَّأَ وَصَلَّى ثُمَّ عَادَ إِلَى مَجْلِسِهِ فَلَمَّا حَضَرَتِ الْعَصْرُ قَامَ فَتَوَضَّأَ وَصَلَّى ثُمَّ عَادَ إِلَى مَجْلِسِهِ فَلَمَّا حَضَرَتِ الْمَغْرِبُ قَامَ فَتَوَضَّأَ وَصَلَّى ثُمَّ عَادَ إِلَى مَجْلِسِهِ فَقُلْتُ أَصْلَحَكَ اللَّهُ أَفَرِيضَةٌ أَمْ سُنَّةٌ الْوُضُوءُ عِنْدَ كُلِّ صَلاَةٍ قَالَ أَوَ فَطِنْتَ إِلَىَّ وَإِلَى هَذَا مِنِّي فَقُلْتُ نَعَمْ . فَقَالَ لاَ لَوْ تَوَضَّأْتُ لِصَلاَةِ الصُّبْحِ لَصَلَّيْتُ بِهِ الصَّلَوَاتِ كُلَّهَا مَا لَمْ أُحْدِثْ وَلَكِنِّي سَمِعْتُ رَسُولَ اللَّهِ ـ ﷺ ـ يَقُولُ " مَنْ تَوَضَّأَ عَلَى كُلِّ طُهْرٍ فَلَهُ عَشْرُ حَسَنَاتٍ " . وَإِنَّمَا رَغِبْتُ فِي الْحَسَنَاتِ .