‘Urwah reported: Aisha, may Allah be pleased with her, said, “No one had better character than the Messenger of Allah, peace and blessings be upon him. No one from his companions or his family called upon him but that he would say: I am at your service. For this reason, Allah Almighty revealed the verse: Verily, you are upon great moral character.” (68:4)
Source: Dalā’il al-Nubuwwah 119
عَنْ عُرْوَةَ عَنْ عَائِشَةَ رَضِيَ اللَّهُ عَنْهَا قَالَتْ مَا كَانَ أَحْسَنُ خُلُقًا مِنْ رَسُولِ اللَّهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ مَا دَعَاهُ أَحَدٌ مِنْ أَصْحَابِهِ وَلَا مِنْ أَهْلِهِ إِلَّا قَالَ لَبَّيْكَ وَلِذَلِكَ أَنْزَلَ اللَّهُ عَزَّ وَجَلَّ وَإِنَّكَ لَعَلَى خُلُقٍ عَظِيمٍ
119 دلائل النبوة لأبي نعيم الأصبهاني