Prayer (Kitab Al-Salat): Details of Commencing Prayer
Dawud :: Book 3 : Hadith 925
Narrated Suhayb:
I passed by the Apostle of Allah (peace_be_upon_him) who was praying. I saluted him and he returned it by making a sign.
The narrator said: I do not know but that he said: He made a sign with his finger. This is the version reported by Qutaybah.