Sayyiduna Abu Dharr al-Ghifari (may Allah be pleased with him) reports this as a marfu' hadith (The Prophet (peace and blessings be upon him) said:) "The treasure that Allah Almighty mentioned in His Book was a tablet of pure gold, on which was written: I am amazed at the one who has certainty in Divine decree and yet becomes distressed; I am amazed at the one who remembers Hell and still laughs; I am amazed at the one who remembers death and then becomes heedless. There is no god but Allah, and Muhammad (peace and blessings be upon him) is the Messenger of Allah."
Al-Bazzar recorded it through Bishr bin al-Mundhir from al-Harith bin Abdullah al-Yahsubi; I do not know either of them. The remaining narrators of this report are thiqat (trustworthy).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب التفسير / 11151