It is narrated from Abu Huraira (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Every prayer in which Umm al-Kitab (Al-Fatiha) is not recited is incomplete, it is incomplete."
Hadith Referenceمسند الإمام الشافعي / كتاب الصلاة / 212
Hadith Takhrijأخرجہ مسلم، الصلاۃ، باب وجوب قراءۃ الفاتحۃ فی کل رکعۃ... الخ: 395۔