The Prophet ﷺ said, "Whoever performs ablution and does it well, then says three times, 'I bear witness that there is no god but Allah alone, with no partner, and that Muhammad is His servant and messenger,' the eight gates of Paradise will be opened for him, and he may enter through whichever of them he wishes."
حدثنا معاوية بن عمرو حدثنا زائدة حدثنا عمرو بن عبد الله بن وهب حدثنا زيد العمي
عن النبي ﷺ قال من توضأ فأحسن الوضوء ثم قال ثلاث مرات أشهد أن لا إله إلا الله وحده لا شريك له وأن محمدا عبده ورسوله فتحت له من الجنة ثمانية أبواب من أيها شاء دخل
Its chain of transmission is daif because of Zayd bin Hawari Ammi, whom Tirmidhi weakened in 1/78, no. 55, in the chapter on purification, on what is said after wudu. It is also found in Nasai, 1/93, no. 148. They mentioned other narrations of it and graded them sahih, so the hadith rises to the level of hasan.