Muhammad (Ibn Sirin) narrates: I was informed that Ibn Mas'ud (may Allah be pleased with him) said: When I came to the Messenger of Allah (peace and blessings be upon him) on my return from Abyssinia, I went to greet him and found him praying. I greeted him with salam, and he (peace and blessings be upon him) gestured with his head.
This is the preserved (mahfuz) version, and it is mursal.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3408