(a) Al-Qasim reports from Sayyidah Aishah (may Allah be pleased with her) that she used to give only one salam, and that too facing forward, and she would say: 'As-salamu alaykum' (Peace be upon you).
(b) It is also reported from Anas bin Malik, Samurah bin Jundub and Salamah bin al-Akwa' (may Allah be pleased with them), and all of them narrate it from the Prophet (peace and blessings be upon him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2986