Narrated Abu Huraira Radiallahu Anhu:

Rasulullah Sallallahu Allahi Wa Sallam said, “There are two expressions which are very easy for the tongue to say, but they are very heavy in the balance and are very dear to The Beneficent (Allah), and they are, 

Subhan Allahil Azim and Subhan Allahi Wa Bihamdihi.”

حَدَّثَنَا زُهَيْرُ بْنُ حَرْبٍ، حَدَّثَنَا ابْنُ فُضَيْلٍ، عَنْ عُمَارَةَ، عَنْ أَبِي زُرْعَةَ، عَنْ أَبِي هُرَيْرَةَ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ ‏

‏ كَلِمَتَانِ خَفِيفَتَانِ عَلَى اللِّسَانِ، ثَقِيلَتَانِ فِي الْمِيزَانِ، حَبِيبَتَانِ إِلَى الرَّحْمَنِ،

سُبْحَانَ اللَّهِ الْعَظِيمِ، سُبْحَانَ اللَّهِ وَبِحَمْدِهِ ‏”

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Sahih al-Bukhari 6406
In-book : Book 80, Hadith 101
USC-MSA web (English) : Vol. 8, Book 75, Hadith 415 (deprecated)

Note:

If you read the Hadith carefully, these Tasbeah are not meant to be recited together. Rather,

سُبْحَانَ اللَّهِ الْعَظِيمِ 

Subhan Allahil Azim is one itself

and 

سُبْحَانَ اللَّهِ وَبِحَمْدِهِ

Subhan Allahi Wa Bihamdihi is another by itself.

The Hadith didn’t make them both a combined Tasbeah.
I used to combine both until I read the Hadith myself and notice that they actually are seperate Tasbeah. 

And Allah knows best.
May Allah make our scale of good deeds heavy.