Ibn Mas'ud, Ibn 'Umar and Anas (May Allah be pleased with them) said:
The Prophet (ﷺ) said, "For every one who breaks his covenant, there will be a (huge) flag on the Day of Resurrection and it will be said: 'This flag proclaims a breach of covenant by so-and-so."'[Al-Bukhari and Muslim]. (DE)
App reference (DE): Book 18, Hadith 75 (DE)
Arabic/English book reference (DE): Book 18, Hadith 1585 (DE)