Al-Ghazali reported: Ali, may Allah ennoble his face, when he saw the decorations of the Nabataeans in Iraq on the day of Eid, he said, “What is this they are showing?” They said, “O commander of the faithful, this is their day of celebration.” Ali said, “Every day in which Allah Almighty is not disobeyed is our celebration.”
Source: Iḥyā’ Ulūm al-Dīn 4/289
عن الغزالي وقال علي كرم الله وجهه لما رأى زينة النبط بالعراق في يوم عيد ما هذا الذي أظهروه قالوا يا أمير المؤمنين هذا يوم عيد لهم فقال: كُلُّ يَوْمٍ لا يَعْصِي اللَّهَ عَزَّ وَجَلَّ الْعَبْدُ فِيهِ فَهُوَ لنا عِيدٌ
4/289 إحياء علوم الدين كتاب التوحيد والتوكل