Jami` at-Tirmidhi 55

Umar bin Al-Khattab narrated that :Allah's Messenger said: 'Whoever performs Wudu, making Wudu well, then says: (Ashhadu an la ilaha illallah, wahdahu la sharika lahu, wa ashhadu anna Muhammadan-abduhu wa rasuluhu, Allahummajalni minat tawwabin, waj'alni minal mutatahhirin) 'I testify that none has the right to be worshipped but Allah Alone, there are no partners for Him. And I testify that Muhammad is His servant and Messenger. O Allah! Make me among the repentant, and make me among those who purify themselves.' Then eight gates of Paradise are opened for him, that may enter by whichever of them wishes