Sa'id bin Jubayr (may Allah have mercy on him) says that a (Muslim) man from the tribe of Khuza'ah was in Makkah and fell ill; his name was Damrah bin al-Is bin Damrah bin Zinba'. He ordered his family to take him to Madinah. They lifted him onto a bedstead and set out towards Madinah. When they reached al-Tan'im, this man died during the journey, and at that time this noble verse was revealed: "And whoever leaves his home as an emigrant to Allah and His Messenger and then death overtakes him, his reward has become incumbent upon Allah" [Surah al-Nisa: 100]. This same explanation was given by al-Hasan al-Basri (may Allah have mercy on him) and other commentators.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 17761