His saying: 'That He may question the truthful ones,' meaning: the prophets, 'about their truthfulness,' that is: about their conveyance of the message from Allah to their people.
قَوْله: ﴿ليسئل الصَّادِقين﴾ يَعْنِي: النَّبِيين ﴿عَن صدقهم﴾ أَيْ: عَنْ تَبْلِيغِ الرِّسَالَةِ إِلَى قَومهمْ من الله.