Jami` at-Tirmidhi 188
جامع الترمذي#188Da'ifIbn Abbas narrated that :the Prophet said: "Whoever combines two prayers without any excuse then he has committed something from the major sins
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirVery Daif
Al-AlbaniVery Daif
Bashar Awad MaaroufDaif
In-book reference: 2:40