The Prophet said: "Whoever performs ablution and does it well, then says three times: 'Ashhadu an la ilaha illallah wahdahu la sharika lahu, wa ashhadu anna Muhammadan ʿabduhu wa rasuluhu (I bear witness that none has the right to be worshipped but Allah alone, with no partner, and I bear witness that Muhammad is His slave and His Messenger),' eight gates of Paradise will be opened for him; whichever one he wants he may enter." (Da'if) Another chain with similar wording. (Using translation from Ibn Mājah 469)
عَنِ النَّبِيِّ ﷺ قَالَ مَنْ تَوَضَّأَ فَأَحْسَنَ الْوُضُوءَ ثُمَّ قَالَ ثَلَاثَ مَرَّاتٍ أَشْهَدُ أَنْ لَا إِلَهَ إِلَّا اللهُ وَحْدَهُ لَا شَرِيكَ لَهُ وَأَنَّ مُحَمَّدًا عَبْدُهُ وَرَسُولُهُ فُتِحَتْ لَهُ مِنَ الْجَنَّةِ ثَمَانِيَةُ أَبْوَابٍ مِنْ أَيِّهَا شَاءَ دَخَلَ