It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with him) that a companion of the Messenger of Allah (may Allah be pleased with him) named Suhaib said: I passed by the Messenger of Allah (peace and blessings be upon him) while he was praying. I greeted him with salam, so he responded to me by gesturing. The narrator says: I do not know except this, that he mentioned gesturing with the finger.
Hadith Referenceالفتح الربانی / أبواب الأذ كار الواردة عقب الصلاة / 1940