Jami` at-Tirmidhi Book 10, Hadith 99
The Messenger of Allah said: "The martyrs are five: Those who die of the plague, stomach illness, drowning, being crushed, and the martyr in the cause of Allah"
"I heard my grandfather, the father of my mother, Simak bin Al-Walid Al-Hanadi narrating, that he heard Ibn Abbas narrated, that he heard the Messenger of Allah saying: "Whoever has two predecessors (in death) among my Ummah, then Allah will admit them into Paradise."So Aishah said to him: "What about one from your Ummar who has one precessor?" He (pbuh) said: "And whoever has one predecessor O Muwaffaqqah!" So she said: "What about one who does not have a predecessor from your Ummah?" He said: "I am the predecessor for my Ummah: you will never suffer (in grief) for (the loss of) anyone similar to me."
"Sulaiman bin Surad said to Khalid bin Urfutah - or, Khalid said to Sulaiman - 'Did you hear the Messenger of Allah saying: "Whoever is killed by his stomach then he will not be punished in the grave"?' One of them said to the other: "Yes."