Sahih Muslim Book - 2, Hadith - 554

و حَدَّثَنَاه أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ حَدَّثَنَا زَيْدُ بْنُ الْحُبَابِ حَدَّثَنَا مُعَاوِيَةُ بْنُ صَالِحٍ عَنْ رَبِيعَةَ بْنِ يَزِيدَ عَنْ أَبِي إِدْرِيسَ الْخَوْلَانِيِّ وَأَبِي عُثْمَانَ عَنْ جُبَيْرِ بْنِ نُفَيْرِ بْنِ مَالِكٍ الْحَضْرَمِيِّ عَنْ عُقْبَةَ بْنِ عَامِرٍ الْجُهَنِيِّ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ فَذَكَرَ مِثْلَهُ غَيْرَ أَنَّهُ قَالَ مَنْ تَوَضَّأَ فَقَالَ أَشْهَدُ أَنْ لَا إِلَهَ إِلَّا اللَّهُ وَحْدَهُ لَا شَرِيكَ لَهُ وَأَشْهَدُ أَنَّ مُحَمَّدًا عَبْدُهُ وَرَسُولُهُ.

It was narrated from 'Uqbah bin 'Amir Al-Juhani that the Messenger of Allah (s.a.w) said:... and he mentioned a similar report (as no. 553), except that he said: "Whoever performs Wudu' then says: 'Ash-hadu An la ilaha illallah Wahdahu La Sharika Lahu, Wa Anna Muhammadan 'Abduhu Wa Rasuluh (none has the right to be worshiped but Allah alone, with no partner or associate, and I bear witness that Muhammad is His slave and Messenger.)'"