Hz. Sawban (may Allah be pleased with him) narrates: “The Messenger of Allah (peace and blessings be upon him) said: ‘Be upright in all matters; do not deviate. But you will not be able to do this perfectly. So know that your best deed is prayer. Only a true believer can maintain ablution properly.’”
Source: Muwatta, Book of Qur’an, Chapter on Prayer
Narrator: Hz. Sawban (may Allah be pleased with him)