Abdullah ibn Shawdhab reported: We were with Al-Hasan al-Basri, may Allah have mercy on him, and he heard a man speaking during Eid. Al-Hasan said, “Every day in which Allah Almighty is not disobeyed is a celebration.”
Source: Musalsal al-ʻĪdayn 28
عَنْ عَبْدِ اللَّهِ بْنِ شَوْذَبٍ قَالَ كُنَّا عِنْدَ الْحَسَنِ الْبَصْرِيِّ رحمه الله فَسَمِعَ رَجُلا يَقُولُ عِنْدَ الْعِيدِ فَقَالَ الْحَسَنُ كُلُّ يَوْمٍ لا يَعْصِي اللَّهَ عَزَّ وَجَلَّ الْعَبْدُ فِيهِ فَهُوَ عِيدٌ
28 كتاب مسلسل العيدين لللخطيب البغدادي