The complete hadith is reported from Sayyiduna Itban bin Malik al-Ansari (may Allah be pleased with him) about the prayer of the Messenger of Allah (peace and blessings be upon him) which the Messenger of Allah (peace and blessings be upon him) led for them. He says: Then he (peace and blessings be upon him) gave the salam, and when he had given the salam, we gave the salam.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2998