Is it permissible for the one praying behind the Imam (ma'mum) to recite more than one surah in a non-audible prayer if he finishes his surah before the Imam, or must he remain silent?

The majority of jurists are of the opinion that it is permissible to recite more than one Surah in a single unit (rak'ah) of prayer, based on what Al-Bukhari and Muslim narrated from Ibn Mas'ud, who mentioned twenty Surahs from the Mufassal, that the Messenger of Allah, may Allah bless him and grant him peace, used to combine two Surahs from them in each rak'ah. Therefore, there is no objection to reciting more than one Surah in a rak'ah.