Oneness, Uniqueness of Allah (Tawheed)
حَدَّثَنِي أَحْمَدُ بْنُ إِشْكَابٍ، حَدَّثَنَا مُحَمَّدُ بْنُ فُضَيْلٍ، عَنْ عُمَارَةَ بْنِ الْقَعْقَاعِ، عَنْ أَبِي زُرْعَةَ، عَنْ أَبِي هُرَيْرَةَ ـ رضى الله عنه ـ قَالَ قَالَ النَّبِيُّ صلى الله عليه وسلم " كَلِمَتَانِ حَبِيبَتَانِ إِلَى الرَّحْمَنِ، خَفِيفَتَانِ عَلَى اللِّسَانِ، ثَقِيلَتَانِ فِي الْمِيزَانِ سُبْحَانَ اللَّهِ وَبِحَمْدِهِ، سُبْحَانَ اللَّهِ الْعَظِيمِ " .Narrated Abu Huraira:The Prophet (ﷺ) said, "(There are) two words which are dear to the Beneficent (Allah) and very light (easy) for the tongue (to say), but very heavy in weight in the balance. They are: ''Subhan Allah wa-bi hamdihi'' and ''Subhan Allah Al-`Azim." (see Hadith)
From Sahih al-Bukhari, whose reports the scholars accept as authentic.