Mishkat al-Masabih 2300
Abu Dharr said that God’s messenger was asked what words were most excellent and replied, “What God has chosen for His angles:
Glory be to God and I begin with praise of Him.” 

Muslim transmitted it.
وَعَنْ أَبِي ذَرٍّ قَالَ: سُئِلَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَيُّ الْكَلَامِ أَفْضَلُ؟ قَالَ: 
" مَا اصْطَفَى اللَّهُ لِمَلَائِكَتِهِ: سُبْحَانَ اللَّهِ وَبِحَمْدِهِ ". رَوَاهُ مُسلم