It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) offered a funeral prayer, said four takbirs over it, and gave a single salam. It is reported from Ata' bin al-Sa'ib (may Allah have mercy on him) as mursal that the Prophet (peace and blessings be upon him) offered the funeral prayer with a single salam to one side.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6982
Umayr bin Sa'id said: I offered the funeral prayer over Yazid bin Mukaffaf behind Ali bin Abi Talib (may Allah be pleased with him), and he said four takbirs and gave a single salam.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6983
Nafi' (may Allah have mercy on him) narrates from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that whenever he prayed the funeral prayer, he would give the salam only to the right.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6985
Khalid bin Yazid bin Abi Malik narrates from his father, who said: I saw Wathilah bin al-Asqa' (may Allah be pleased with him); he would give a single salam in the funeral prayer.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6987