It is narrated from Sayyiduna Ubadah bin al-Samit (may Allah be pleased with him) that he saw a man praying who was completing neither his bowing nor his prostrations. Ubadah (may Allah be pleased with him) came to that man, took hold of his hand and (addressing the other people) said: Do not follow his prayer, for "There is no prayer without Surah al-Fatihah." If you are behind the imam, recite it within yourself, and if you are praying alone, keep your voice limited to your own ears, and do not disturb those on your right and left (by reciting aloud). The position of Ubadah (may Allah be pleased with him) on this is well known. Among them is Ubayy bin Ka'b (may Allah be pleased with him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2935