Sahih Muslim , Book 1, Hadith 283 (In-Book) ⓘ
It is narrated on the authority of Anas that the Messenger of Allah said: "The Hour (Resurrection) will not occur as long as anyone says: 'Allah, Allah.'"
حَدَّثَنَا عَبْدُ بْنُ حُمَيْدٍ، أَخْبَرَنَا عَبْدُ الرَّزَّاقِ، أَخْبَرَنَا مَعْمَرٌ، عَنْ ثَابِتٍ، عَنْ أَنَسٍ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " لاَ تَقُومُ السَّاعَةُ عَلَى أَحَدٍ يَقُولُ اللَّهُ اللَّهُ " .
also referenced under: Hadith 148 (Reference) & Book 1, Hadith 274 (USC-MSA)