Musnad Abu Ya'la al-Mawsili 117:172

Al-Hasan ibn al-Sabah al-Bazzar narrated to us, Mu'ammal ibn Isma'il narrated to us, from Hammad, Thabit narrated to us, from Anas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever asks for martyrdom sincerely from his heart, Allah will grant him the reward of a martyr, even if he dies upon his bed."