Narrated by Abu Huraira (Radhiallaho anho):
The Prophet (sallallaahu 'alaihi wasallam) said, "Martyrs are
those who die because of drowning, plague, an abdominal
disease, or of being buried alive by a falling building." And
then he (sallallaahu 'alaihi wasallam) added, "If the people
knew the reward for the Zuhr prayer in its early time, they
would race for it. If they knew the reward for the 'Isha' and
the Fajr prayers in congregation, they would join them even if
they had to crawl. If they knew the reward for the first row,
they would draw lots for it."

Bukhari Vol. 1 : No. 688