Narrated 'Abdullah bin Mas'ud:
Sa'd bin Mu'adh came to Mecca with the intention of performing 'Umra, and stayed at the house of Umaiya bin Khalaf Abi Safwan, for Umaiya himself used to stay at Sa'd's house when he passed by Medina on his way to Sham. Umaiya said to Sad, "Will you wait till midday when the people are (at their homes), then you may go and perform the Tawaf round the Ka'ba?" So, while Sad was going around the Ka'ba, Abu Jahl came and asked, "Who is that who is performing Tawaf?" Sad replied, "I am Sad." Abu Jahl said, "Are you circumambulating the Ka'ba safely although you have given refuge to Muhammad and his companions?" Sad said, "Yes," and they started quarreling. Umaiya said to Sad, "Don't shout at Abi-l-Hakam (i.e. Abu Jahl), for he is chief of the valley (of Mecca)."

Sad then said (to Abu Jahl). 'By Allah, if you prevent me from performing the Tawaf of the Ka'ba, I will spoil your trade with Sham." Umaiya kept on saying to Sad, "Don't raise your voice." and kept on taking hold of him. Sad became furious and said, (to Umaiya), "Be away from me, for I have heard Muhammad saying that he will kill you." Umaiya said, "Will he kill me?" Sad said, "Yes." Umaiya said, "By Allah! When Muhammad says a thing, he never tells a lie." Umaiya went to his wife and said to her, "Do you know what my brother from Yathrib (i.e. Medina) has said to me?" She said, "What has he said?" He said, "He claims that he has heard Muhammad claiming that he will kill me."

She said, By Allah! Muhammad never tells a lie." So when the infidels started to proceed for Badr (Battle) and declared war (against the Muslims), his wife said to him, "Don't you remember what your brother from Yathrib told you?" Umaiya decided not to go but Abu Jahl said to him, "You are from the nobles of the valley of Mecca), so you should accompany us for a day or two." He went with them and thus Allah got him killed.

Often Allah seems to be very anxious to fulfill Muhammad's will ... as Aisha observed on some occasions. We see Muhammad announcing that he would kill Umaiya. Was it really Allah or could it be that not only Sa`d but more of Muhammad's people knew that the execution of Umaiya was Muhammad express wish which they then hastened to fulfill?

In any case, Muhammad expressed his plan to kill him and it happened.

One of many who were killed after there was some request or order by Muhammad to do so. This one is different as it happens during an official battle and being killed on the battle field is not the same as a night time execution squad but nevertheless he seems to have been singled out and Muhammad's soldiers might have been instructed to have special attention to see to his death.

We don't know for sure, but it fits the pattern of the many other assassinations of Muhammad's personal enemies.

Ironically, the book in Bukhari out of which this hadith is taken is titled "Virtues and Merits of the Prophet (pbuh) and his Companions".