"Until, when the messengers gave up hope and thought that they had been denied." Al-Hasan used to recite it with the heavy vocalization (kudh-dhibu - had been belied). Its interpretation is: "Until, when the messengers gave up hope," meaning: the messengers despaired that their people would respond to them, due to something they had learned from Allah. "And they thought," meaning: they knew; that is, the messengers knew that they had been denied—a denial after which the people would never believe. They then sought victory against their people by praying against them; so He responded to them and destroyed them.
Ibn Abbas used to recite it (kudh-ibu - had been denied) with light vocalization, and its interpretation is: "Until, when the messengers gave up hope..."
﴿حَتَّى إِذا استيئس الرُّسُلُ وَظَنُّوا أَنَّهُمْ قَدْ كُذِبُوا﴾ كَانَ الْحَسَنُ يَقْرَؤُهَا بِالتَّثْقِيلِ (كُذِّبُوا) وَتَفْسِيرُهَا: حَتَّى إِذَا اسْتَيْئَسَ الرُّسُلُ؛ أَيْ: يَئِسَ الرُّسُلُ أَنْ يُجِيبَهُمْ قَوْمُهُمْ لشيءٍ قَدْ عَلِمُوهُ مِنْ قِبَلِ اللَّهِ وَظَنُّوا؛ أَيْ: عَلِمُوا؛ يَعْنِي: الرُّسُلَ أَنَّهُمْ قَدْ كُذِبُوا، التَّكْذِيبُ الَّذِي لَا يُؤْمِنُ الْقَوْمُ بَعْدَهُ أَبَدًا، اسْتَفْتَحُوا عَلَى قَوْمِهِمْ بِالدُّعَاءِ عَلَيْهِمْ؛ فَاسْتَجَابَ لَهُمْ فَأَهْلَكَهُمْ.
وَكَانَ ابْنُ عباسٍ يَقْرَؤُهَا (كُذِبُوا) خَفِيفَةً، وَتَفْسِيرُهَا: حَتَّى إِذَا اسْتَيْئَسَ
