Sayyiduna Suhayb (may Allah be pleased with him) narrates: the Messenger of Allah (peace and blessings be upon him) was praying. I passed by him (peace and blessings be upon him) and greeted him (peace and blessings be upon him) with salam. He (peace and blessings be upon him) replied with a gesture. Layth said: I think he said: He gestured with his finger.
It has been narrated about this incident through a chain containing irsal (a break) that he gestured with his hand, without any doubt.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3400