the Prophet said: "Whoever combines two prayers without any excuse then he has committed something from the major sins." (Using translation from Tirmidhī 188)
عَنِ النَّبِيِّ ﷺ قَالَ «مَنْ جَمَعَ بَيْنَ صَلَاتَيْنِ مِنْ غَيْرِ عُذْرٍ فَقَدْ أَتَى بَابًا مِنْ أَبْوَابِ الْكَبَائِرِ»