Question Summary:
Hadith on combining two prayers without an excuse

Question Detail:

Assalamu Alaikum
 
I am writing to ask about the hadith:
"Ibn Abbas (radiallahu Anho) narrates that he heard the prophet (saw) saying:
"a person who combines two salaats without any strong excuse reaches one of the doors of kabaair (major sins)"
i would like to know if this hadith is strong or weak and which hadith book it is  found in?

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
The Hadith in reference is narrated in Sunan al-Tirmidhi. The Arabic text is reproduced below:
عَنْ ابْنِ عَبَّاسٍ، عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «مَنْ جَمَعَ بَيْنَ الصَّلَاتَيْنِ مِنْ غَيْرِ عُذْرٍ فَقَدْ أَتَى بَابًا مِنْ أَبْوَابِ الكَبَائِرِ (سنن الترمذي، باب ما جاء في الجمع بين الصلاتين) 
Ibn Abaas Radhiyallahu Anhu narrates that Nabi Sallallahu Alaihi Wa Sallam said, “Whosoever combines two prayers without an excuse, has reached a door from the doors of Kabaair (major sins) (Sunan al-Tirmidhi)
Despite the chain of this particular narration being weak, there are various proofs from Quran and Hadith that support this Hadith.  Consider the following authentic narration that appears in the Muwatta of Imam Mohammad[1]:
 
 
عَنْ عُمَرَ بْنَ الْخَطَّابِ , أَنَّهُ «كَتَبَ فِي الآفَاقِ، يَنْهَاهُمْ أَنْ يَجْمَعُوا بَيْنَ الصَّلاتَيْنِ، وَيُخْبِرُهُمْ أَنَّ الْجَمْعَ بَيْنَ الصَّلاتَيْنِ فِي وَقْتٍ وَاحِدٍ كَبِيرَةٌ مِنَ الْكَبَائِرِ (موطاء امام محمد، ج 1، ص 82، المكتبة العلمية)
 
Umar Radhiyallah Anhu wrote to the distants areas preventing them from combining two prayers and informing them that combining two prayers in one time is from among the major sins.  (Muwatta Imam Mohammad)
 
After narrating the Hadith, Imam Tirmidhi states that the scholars of Deen practice upon this Hadith. [2]
And Allah Ta’āla Knows Best
Abdul Azīm bin Abdur Rahman,
Student Darul Iftaa
U.S.A.
Checked and Approved by,
Mufti Ebrahim Desai.