Narrated Ibn `Abbas:
Regarding the Verse: "And say not to anyone who offers you peace (by accepting Islam), You are not a believer." There was a man amidst his sheep. The Muslims pursued him, and he said (to them) "Peace be on you." But they killed him and took over his sheep. Thereupon Allah revealed in that concern, the above Verse up to:-- "...seeking the perishable good of this life." (4.94) i.e. those sheep.
USC-MSA web (English) reference: Vol. 6, Book 60, Hadith 115
Arabic reference: Book 65, Hadith 4591