Musnad Ahmad 1018:39

Yazid narrated to us, Hisham bin Abi Abdullah al-Dastawa'i narrated to us, from Yahya bin Abi Kathir, from Abu Salam, that a man narrated to him that he heard the Prophet, peace and blessings of Allah be upon him, saying: "Bakh, bakh (an expression of admiration) for five things! How heavy they are in the scale!" A man said: "What are they, O Messenger of Allah?" He said: "La ilaha illa Allah (There is no god but Allah), Allahu Akbar (Allah is the Greatest), Subhan Allah (Glory be to Allah), Al-Hamdulillah (Praise be to Allah), and a righteous child who dies and his father seeks reward for him." "Five things: whoever fears Allah through them, being certain, will enter Paradise: whoever testifies that there is no god but Allah and that Muhammad is His servant and Messenger, and is certain of death, the resurrection, and the reckoning."