Musnad Ahmad 30:1486

Hassan narrated to us, Ibn Lahi'ah narrated to us, Abu Yunus narrated to us, from Abu Hurairah, from the Messenger of Allah (peace and blessings of Allah be upon him), that he said: "None of you should wish for death, nor pray for it before it comes to him, unless he is confident in his deeds. For if one of you dies, his deeds are cut off from him. And indeed, the life of a believer does not increase him in anything except good."