Sunan Ibn Majah Book 33, Hadith 145
the Messenger of Allah (ﷺ) told them: "One of the slaves of Allah said: 'Ya Rabb! Lakal-hamdu kama yanbagi li-jalali Wajhika wa li 'azima sultanika (O Lord, to You is praise as befits the Glory of Your Face and the greatness of Your Might.)' The angels were uncertain and did not know how to write this down, so they ascended to heaven and said: 'O our Lord, Your slave has said a word that we do not know how to write down.' Allah said - and He knows best what His slave said - 'What did My slave say?' They said: 'O Lord, he said "Ya Rabb! Lakal-hamdu kama yanbagi li-jalali Wajhika wa li'azima sultanika (O Lord, to You is praise as befits the Glory of Your Face and the greatness of your Might).'" Allah said to them: 'Write it down as My slave said it, until he meets Me and I shall reward him for it.'"
"I heard the Messenger of Allah (ﷺ) say: 'The best of remembrance is La ilaha illallah (None has the right to be worshipped but Allah), and the best of supplication is Al-Hamdu Lillah (praise is to Allah).'"
his father said: "I prayed with the Prophet (ﷺ) and a man said: 'Alhamdu lillahi hamdan kathiran tayyiban mubarakan fihi (Praise is to Allah, much, good and blessed praise).' When the Prophet (ﷺ) finished praying, he said: 'Who said that?' The man said: 'It was me, but I did not mean anything but good.' He said: 'The gates of heaven were opened because of it and nothing prevented it from reaching the Throne.'"