Abu Malik al-Ash'ari (may Allah be pleased with him) said: I heard the Messenger of Allah (peace and blessings be upon him); he (peace and blessings be upon him) said: "Whoever goes out for jihad in the way of Allah, seeking Allah's pleasure, affirming His promise and believing in His messengers, Allah, the Lord of Might, is the guarantor of this servant that, in whatever way He causes him to die in the army, He will admit him to Paradise. He remains in Allah's guarantee, even if his absence is long. Then Allah, the Lord of Might, will return him to his home safe and sound, with reward and spoils of war." The narrator said: "Whoever dies in the way of Allah, or is martyred, or is thrown by his horse or camel, or is stung by something venomous, or dies on his very bed, he is a martyr and Paradise is his."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18537