The Prophet ﷺ said regarding the verse "We shall surely question them all about what they used to do" [Hijr 15:92–93], "It refers to the statement, 'There is no god but Allah.'"
حدثنا أحمد بن عبدة الضبي حدثنا معتمر بن سليمان عن ليث بن أبي سليم عن بشر
عن النبي ﷺ في قوله {لنسألنهم أجمعين عما كانوا يعملون} قال عن قول لا إله إلا الله
No references are available.
Its chain is daif. Abu Yaala also recorded it, no. 4058, through the hadith of Layth bin Abu Salim, with the same wording. Layth bin Abu Salim is daif, and there is another version of it in Abu Naeem's Hilyah (3/95), whose chain is also daif, and the mawquf version is likewise daif.