Tafsir of Ya seen 36:48

"And they say" is a conjunctive clause to the preceding conditional one, serving to express their denial of the Resurrection, which is the source of all evil. The Prophet—may Allah bless him and grant him peace—ceaselessly promised them this, and what is brought to their minds is what preceded regarding the commandments. Therefore, they used the demonstrative for something near in their saying, "When is this promise?" meaning the promise of the Resurrection. It is permitted that this is by way of mockery, implying: When will that happen and be realized in the external world?

"If you are truthful" regarding what you say and promise, so inform us of that. The address is to the Messenger of Allah—may Allah bless him and grant him peace—and the believers, since they too used to recite to them the verses that indicate it and command belief in it. It is as if he did not consider it to be an evil for them, and for this reason, they expressed it as a "promise" (wa'd) rather than a "threat" (wa'id). It is said: This is because they claimed that they would have the best outcome with Allah the Exalted if the Resurrection were to be realized, on the premise that the verse refers to others than the atheists.