Sayyiduna Ubadah bin al-Samit (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "There is no prayer for the person who does not recite Surah al-Fatihah."
Likewise Imam al-Shafi'i (may Allah have mercy on him) and al-Humaydi narrated it from Sufyan bin Uyaynah: "Whoever does not recite Surah al-Fatihah has no prayer."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2364