Hasan on Islam: Religion is to worship Allah, at peace with others

Isra’il Abi Musa reported: Hasan al-Basri, may Allah have mercy on him, said, “What is Islam? It is that you surrender your heart to Allah Almighty, and that every Muslim and protected person is safe from you.”

Source: al-Zuhd wal-Raqā’iq 644

عَنْ إِسْرَائِيلَ أَبِي مُوسَى قَالَ الحسن البصري رحمه الله مَا الْإِسْلَامُ أَنْ يُسْلِمَ قَلْبُكَ لِلَّهِ تَعَالَى وَأَنْ يَسْلَمَ مِنْكَ كُلُّ مُسْلِمٍ وَذِي عَهْدٍ

644 الزهد والرقائق لابن المبارك