Khaythamah reported: Abdullah ibn Mas’ud, may Allah be pleased with him, said, “By the One besides whom there is no God, a believing servant is not given anything better than good thoughts about Allah Almighty. By the One besides whom there is no God, a servant does not improve his opinion of Allah Almighty except that Allah will give him what he assumes. That is because all good is in His hands.”
Source: Ḥusn al-Ẓan Billāh 83
عَنْ خَيْثَمَةَ قَالَ قَالَ عَبْدُ اللَّهِ بن مسعود رضي الله عنه وَالَّذِي لَا إِلَهَ غَيْرُهُ مَا أُعْطِيَ عَبْدٌ مُؤْمِنٌ شَيْئًا خَيْرًا مِنْ حُسْنِ الظَّنِّ بِاللَّهِ عَزَّ وَجَلَّ وَالَّذِي لَا إِلَهَ غَيْرُهُ لَا يُحْسِنُ عَبْدٌ بِاللَّهِ عَزَّ وَجَلَّ الظَّنَّ إِلَّا أَعْطَاهُ اللَّهُ عَزَّ وَجَلَّ ظَنُّهُ ذَلِكَ بِأَنَّ الْخَيْرَ فِي يَدِهِ
83 حسن الظن بالله لابن أبي الدنيا