Sunan at-Tirmithiy كتاب الصلاة باب ما جاء كيف الجلوس فى التشهد
The Prophet, peace and blessings of God be upon him, said to Abū-Bakr, "I passed by you as you were reciting (Qur'ān or prayer)1 in a low voice." So he replied, "It was audible to the One with whom I was conversing intimately." He, peace and blessings of God be upon him, said, "Raise your voice slightly." He said to 'Umar, "I passed by you as you were reciting in a raised voice." He ('Umar) replied, "I rouse the sleepy and repel Satan." He, peace and blessings of God be upon him, said, "Lower your voice slightly." Footnotes: (1). i.e., he was praying an audible prayer. Click on ḥadīth to read more
The Prophet, peace and blessings of God be upon him, spent a whole night in voluntary night prayer reciting a single Qur'ānic verse.(1) Footnotes: (1)The verse was "If You should punish them - indeed they are Your servants; but if You forgive them - indeed it is You who is the Exalted in Might, the Wise." (5[alMā'idah]:118) The Prophet, peace and blessings of God be upon him, kept repeating this verse all through the prayer, standing, kneeling and prostrating. Click on ḥadīth to read more
Abdullāh Ibn-Abi-Qays said, "I asked Ā'ishah, 'What was the recitation of the Prophet, peace and blessings of God be upon him, like during the night (1); did he use to recite silently or aloud? She replied, 'Indeed, he did both, sometimes silently and sometimes aloud.' I said, 'Praise be to God who has allowed flexibility in this.'" Footnotes: (1) i.e. during the voluntary night prayer Click on ḥadīth to read more