silent

As-salaamu 'alaikum,Is silent recitation whispered OR in a low voice?

Salaam AlaikumIs there hadith on why surahs are to be recited aloud during first two rakahs for Fajr, Maghrib and Isha Fard prayers, while silently for Dhur, Asr and other Sunnah prayers?I read a hadith that states Proph. Muhammad(SAWS) did it this way, but are there any reasons why he or it is so done?Walaikum Salaam Khan Kabir

Assalamu aalikum wa rahmatu Allahi Ta'ala wa barakatuhu!Is completely silent dhikr without moving tongue or lips acceptable and valid, in situations such as in the train in a non-muslim country, or market?Jazakallahu khayran

Scholars of Islam, As-Salamu `Alaykum wa Rahmatu Allah wa Barakatuh. Allah's Messenger, peace and blessings be upon him, is reported to have said: "Say good or remain silent."; so is excessive talking unlawful in light of this Hadith?