وَيَقُولُونَ مَتَىٰ هَـٰذَا ٱلْوَعْدُ إِن كُنتُمْ صَـٰدِقِينَ
Wayaqooloona mat a h atha alwaAAdu in kuntum sa diqeen a But they [only] ask, "When is this promise to be fulfilled? [Answer this, O you who believe in it,] if you are men of truth!"
 - Mohammad Asad
They ask: "When will this promise be fulfilled, if what you say is true?"
 - Muhammad Farooq-i-Azam Malik
'Still' 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 ask: When will this promise be (fulfilled)? If ye are telling the truth. 5585
 - Abdullah Yusuf Ali