Sayyiduna Uqbah bin Amir (may Allah be pleased with him) heard Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) saying that the Messenger of Allah (peace and blessings be upon him) said: "Whoever performs ablution well and then says: 'Ashhadu an la ilaha illallah wahdahu la sharika lahu, wa anna Muhammadan abduhu wa rasuluh' (I bear witness that there is no god worthy of worship except Allah, alone, without partner, and that Muhammad is His servant and His Messenger), the eight gates of Paradise are opened, and he may enter through whichever he wishes."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 369