Sahih Bukhari Volume 5, Book 64, Hadith 4405

‏"‏ أَلاَ إِنَّ اللَّهَ حَرَّمَ عَلَيْكُمْ دِمَاءَكُمْ وَأَمْوَالَكُمْ، كَحُرْمَةِ يَوْمِكُمْ هَذَا، فِي بَلَدِكُمْ هَذَا، فِي شَهْرِكُمْ هَذَا، أَلاَ هَلْ بَلَّغْتُ ‏"‏‏.‏ قَالُوا نَعَمْ‏.‏ قَالَ ‏"‏ اللَّهُمَّ اشْهَدْ، ثَلاَثًا، وَيْلَكُمْ، أَوْ وَيْحَكُمُ، انْظُرُوا لاَ تَرْجِعُوا بَعْدِي كُفَّارًا، يَضْرِبُ بَعْضُكُمْ رِقَابَ بَعْضٍ

No doubt,! Allah has made your blood and your properties sacred to one another like the sanctity of this day of yours, in this town of yours, in this month of yours." The Prophet added: No doubt! Haven't I conveyed Allah's Message to you? " They replied, "Yes," The Prophet said thrice, "O Allah! Be witness for it." The Prophet added, "Woe to you!" (or said), "May Allah be merciful to you! Do not become infidels after me (i.e. my death) by cutting the necks (throats) of one another."