'Abdullah bin Abi Qays Radiyallahu 'Anhu reports:
"I inquired from 'Aayeshah Radiyallahu 'Anha about the recital of Rasulullah Sallallahu 'Alayhi Wasallam, did he 'recite softly or audibly? She replied: 'He recited in both ways'. I said: 'Alhamdulillaah, (Praise be to, Allah), who has accorded us easiness in the matter"'. (According to the situation whatever was proper, reciting softly or audibly was adopted)
English reference: Book 43, Hadith 300
Arabic reference: Book 44, Hadith 317