It was narrated that Abdullah bin Abi Qais said: “I asked Aishah: “How did the Messenger of Allah (peace be upon him) recite at night- did he recite loudly or silently?” She said: ‘He used to do both; sometimes he recited loudly and sometimes he recited silently.'”
Sunan an-Nasa’I, Vol. 2, Book 20, Hadith 65