the prayer is not valid I one does not recite fatihat al-kitab and something more, sufyan( the narrator) said: This applies to a man who prays alone.
النَّبِيَّ ﷺ قَالَ لاَ صَلاَةَ لِمَنْ لَمْ يَقْرَأْ بِفَاتِحَةِ الْكِتَابِ فَصَاعِدًا قَالَ سُفْيَانُ لِمَنْ يُصَلِّي وَحْدَهُ