The Reward for Glorifying, Praising, Declaring God’s Unity and His Greatness - Section 1 Mishkat al-Masabih 2300
Arabic hadith text
وَعَنْ أَبِي ذَرٍّ قَالَ: سُئِلَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَيُّ الْكَلَامِ أَفْضَلُ؟ قَالَ:" مَا اصْطَفَى اللَّهُ لِمَلَائِكَتِهِ: سُبْحَانَ اللَّهِ وَبِحَمْدِهِ ". رَوَاهُ مُسلم
Translation
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.