Reciting Bismillah softly after Sana

Hazrat Anas (Radiyallahu Anhu) narrated that Rasulullah (Sallallaahu Alaihi Wasallam), Hazrat Abu Bakr (Radiyallahu Anhu) and Hazrat 'Umar (Radiyallahu Anhu) used to start Salah by Alhamdulillahi Rabbil 'aalamin. (Bukhari)

This means that these three people did not recite Bismillahir Rahmaanir Rahim aloud.

[English version of "Après Sanaa lire Bismillah Doucement" – Al Jamiat – Vol.2 No.2]