Sayyiduna Abu al-Darda' (may Allah be pleased with him) narrates this saying of the Prophet (peace and blessings be upon him): "Islam has a distinct light and signs, just as there are markers along a road. Its head and its sum is bearing witness that there is no god but Allah Almighty and that Sayyiduna Muhammad (peace and blessings be upon him) is His servant and Messenger, and establishing prayer, giving zakah and performing ablution completely."
Imam al-Tabarani recorded it in al-Mu'jam al-Kabir.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الإيمان / 111