(Al-Muaminoon) 23 : 9
وَالَّذِينَ هُمْ عَلَىٰ صَلَوَاتِهِمْ يُحَافِظُونَ
And they are those who carefully maintain their prayers.
This verse is repeated in 70: 34. See explanation 2: 62; 7: 205-206 and 16: 110.