Tafsir of Al-Mulk 67:25

"And they say"—out of their excessive insolence and aversion—"when is this promise?" That is, the promised gathering, as indicated by His, the Exalted’s, saying: 'And to Him you will be gathered.'

"If you are truthful"—they address this to the Prophet, may Allah bless him and grant him peace, and to the believers, as they were participants with him, peace and blessings be upon him, in the promise and the recitation of the verses that contain it. The response to the conditional clause is omitted; that is: "If you are truthful in what you report regarding the coming of the Hour and the gathering, then specify its time."