On Thursday, five days before the Prophet (SAW) died, He (SAW) delivered an important sermon to his companions. In it, he (SAW) extolled the superior character of Abu Bakr As-Siddiq (RA) and reiterated his command that Abu (RA) should lead the rest of his companions in congregational prayers. At first, the Prophet (SAW) had wanted to write an important document, one that would contain important final commands. When he (SAW) decided not to write that document, perhaps he (SAW) decided to give a sermon instead.
Upon returning from Hajj in the month of Dhul-Hijjah, the Messenger of Allah (SAW) remained in Al-Madinah for the rest of the month and the months of Al-Muharram and Safar of the year of 10 Hijrah. He (SAW) quickly began to mobilize a huge army, and he (SAW) appointed Usamah ibn Zaid ibn Harithah (RA) to be its leader, ordering him to lead his army to the lands of Al-Balqa and Palestine. It was around that time that the Prophet’s final illness began. It is related that the first signs of his illness appeared at the end of the month of Safar. Some scholars set the exact date of the beginning of his illness as the 22nd of Safar; others believe it was the 29th; and yet others said that he first became ill at the beginning of the month of Rabi’ul Awwal.
The Prophet (SAW) said: “When one commits a sin, a black spot appears on his heart. When he refrains from it, seeks forgiveness, and repents, his heart is polished clean. But if he returns to it, it increases until it covers his heart., and this the Ran which Allah mentioned: ‘No, but on their hearts is the Ran which they earned.’” (Al-Mutaffifin: 14)