Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) narrates: When I returned from Abyssinia, I came to the Messenger of Allah (peace and blessings be upon him) while he was praying. I greeted him with salam, and he (peace and blessings be upon him) replied by gesturing with his head.
Only Abu Ya'la Muhammad bin al-Salt al-Tuzi narrated it (in this way).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3409