Sayyiduna Ubadah bin al-Samit (may Allah be pleased with him) narrates: We were with the Prophet (peace and blessings be upon him) in a gathering, and he (peace and blessings be upon him) said: "Pledge allegiance to me that you will never associate anything with Allah." Then he recited a verse and said: "Whoever fulfils (the pledge) will have a reward; and whoever commits a wrong and is punished for it, that will be an expiation for him; and if someone commits a wrong and it remains concealed, his matter is with Allah: if He wills He forgives him, and if He wills He punishes him."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأشربة والحد فيها / 17592