From Sahih Muslim (Hadith 882):
Abu Huraira reported:The Messenger of Allah (ﷺ) said: One is not credited with having observed the prayer without the recitation (of al-Fatiha). So said Abu Huraira: (The prayer in which) the Messenger of Allah (ﷺ) recited in a loud voice, we also recited that loudly for you (and the prayer in which) he recited inwardly we also recited inwardly for you (to give you a practical example of the prayer of the Holy Prophet)
Reference: Muslim 882