Musannaf Ibn Abi Shayba 1:21

Zayd ibn al-Hubab narrated to us, he said: Mu'awiyah ibn Salih narrated to us, from Rabi'ah ibn Yazid, from Abu Idris al-Khawlani and Abu 'Uthman, from Jubayr ibn Nufayr ibn Malik al-Hadrami, from 'Uqbah ibn 'Amir al-Juhani, that the Messenger of Allah (may Allah bless him and grant him peace) said: "There is no one who performs ablution and perfects the ablution, then prays two rak'ahs, approaching them with his heart and his face, except that Paradise becomes mandatory for him." He (the narrator) said: 'Umar said, "What preceded it is greater than it; it is as if you have just come." The Messenger of Allah (may Allah bless him and grant him peace) said: "Whoever performs ablution and then says, 'I bear witness that there is no god but Allah alone, He has no partner, and I bear witness that Muhammad is His servant and His messenger,' the eight gates of Paradise are opened for him; he may enter through whichever of them he wishes."