Yahya related to me from Malik from Abu'z Zinad from al-Araj fromAbu Hurayra that the Messenger of Allah, may Allah bless him and granthim peace, said, "The Hour will not come until a man passes by thegrave of another and says, 'If only I were in his place.' "
USC-MSA web (English) reference: Book 16, Hadith 54
Arabic reference: Book 16, Hadith 576