What he made inviolable in the farewell sermon
He measured it against the day they were standing in.
فَإِنَّ دِمَاءَكُمْ وَأَمْوَالَكُمْ وَأَعْرَاضَكُمْ بَيْنَكُمْ حَرَامٌ كَحُرْمَةِ يَوْمِكُمْ هَذَا، فِي شَهْرِكُمْ هَذَا، فِي بَلَدِكُمْ هَذَا
Fa-inna dimāʾakum wa amwālakum wa aʿrāḍakum baynakum ḥarāmun ka-ḥurmati yawmikum hādhā, fī shahrikum hādhā, fī baladikum hādhā
Your blood, your property and your honour are sacred among you, like the sacredness of this day of yours, in this month of yours, in this city of yours.
Where this comes from
They were standing in the most protected day, in the most protected month, in the most protected place. He pointed at all three and said: this is what a person is worth. Then: let the one present carry it to the one absent.
The full narration
Narrated `Abdur-Rahman bin Abi Bakra's father:Once the Prophet (ﷺ) was riding his camel and a man was holding its rein. The Prophet (ﷺ) asked, "What is the day today?" We kept quiet, thinking that he might give that day another name. He said, "Isn't it the day of Nahr (slaughtering of the animals of sacrifice)" We replied, "Yes." He further asked, "Which month is this?" We again kept quiet, thinking that he might give it another name. Then he said, "Isn't it the month of Dhul-Hijja?" We replied, "Yes." He said, "Verily! Your blood, property and honor are sacred to one another (i.e. Muslims) like the sanctity of this day of yours, in this month of yours and in this city of yours. It is incumbent upon those who are present to inform those who are absent because those who are absent might comprehend (what I have said) better than the present audience
Source
Ṣaḥīḥ al-Bukhārī · 67
- Agreed upon as authentic (al-Bukhārī / Muslim)