Silsilah as-Sahihah 421 — Only a believer maintains wudu

Sayyiduna Thawban (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "Follow the right path, adopt moderation, act (righteously), and give preference (to the best deeds), and know that your best deed is prayer, and only a believer is the one who guards his ablution."