[20].Surah Taha [Tâ-Hâ]: Ayat 7-8

Ayat 7. And if you speak (the invocation) aloud, then verily, He knows the secret and that which is yet more hidden.

Ayat 8. Allah! Lâ ilâhla illa Huwa (none has the right to be worshipped but He)! To Him belong the Best Names. 

[Tafseer] If thou pronounce the word aloud, (it is no matter): for verily He know what is secret and what is yet more hidden. There are two implications. (1) Whatever you profess, or say aloud, gives no information to Allah: He knows not only what is secret and perhaps unknown to others, but what people take special care to conceal. (2) It docs you no good to make insincere professions: your hidden motives are known to Him, Who alone matters. (3) If you read the Word of Allah, or if you pray to Allah, it is not necessary to raise your voice: in either case, Allah will judge you by your inner thoughts which are like an open book to Him. Allah. there is no god but He! To Him belong the most Beautiful Names. Allah is all-in-all, and the most beautiful things we can think of arc referable to Him. His names refer to His attributes which arc like titles of Honour and Glory.

Hazrat Abu Musa Al-Ashari (May Allah be pleased with him) reported: We accompanied the Messenger of Allah [SAWW](PBUH) in a journey, and when we climbed up a height, we proclaimed aloud: "La ilaha illallah (There is no true god except Allah)'' and "Allahu Akbar (Allah is Greatest).'' The Messenger of Allah [SAWW](PBUH) admonished us saying, "O people, take it easy. He Whom you are calling is not deaf or absent. He is with you (i.e., by His Knowledge), He is Hearing and He is Near.''

[Al-Bukhari Book 35, Chapter 13, Hadith # 6528] 

Lesson : as mentioned above in Surah Taha Ayat ."And if you speak (the invocation) aloud, then verily, He knows" This Hadith tells us that in the pronouncement of the fundamental testification of Islam: "La ilaha illallah (there is no true god except Allah)'' (Tahlil) - and His Magnification: "Allahu Akbar (Allah is Greatest)'' (Takbir) - the voices of the Companions became a bit louder during a journey. The Prophet [SAWW](PBUH) disapproved of it and commanded them not to put themselves to hardship by remembering Allah in a loud voice, and directed to do that calmly in a dignified, low voice.