وَيَقُولُونَ مَتَىٰ هَـٰذَا ٱلْوَعْدُ إِن كُنتُمْ صَـٰدِقِينَ
Wayaqooloona mat a h atha alwaAAdu in kuntum sa diqeen a But they [who reject My messages are wont to] ask, "When is that promise [of God's judgment] to be fulfilled? [Answer this, O you who believe in it,] if you are men of truth!"51
 - Mohammad Asad
They ask: "When will this promise be fulfilled if you are telling the truth?"
 - Muhammad Farooq-i-Azam Malik
They ask 'the believers', 'When will this threat come to pass if what you say is true?'
 - Mustafa Khattab
And they say: When will this promise (be fulfilled), if ye are truthful?
 - Marmaduke Pickthall
They say: "When will this promise come to pass if ye are telling the truth?"
 - Abdullah Yusuf Ali