Al-Matalib al-'Aliyah 3597 — Surah al-An'am

It is narrated from Sayyiduna Abu Bakr al-Siddiq (may Allah be pleased with him) that he asked his companions: "What do you say about these two blessed verses: 'Indeed, those who have said, "Our Lord is Allah," and then remained steadfast' [Surah Fussilat: 30], and 'Those who believe and do not mix their faith with wrongdoing' [Surah al-An'am: 82]?" The Companions said: "'Those who have said, "Our Lord is Allah," and then remained steadfast' means those who affirmed Allah's lordship, then acted according to the requirements of that affirmation and stood firm on Allah's command; while 'those who believe and do not mix their faith with wrongdoing' means those who did not commit any sin after believing." Then Sayyiduna Abu Bakr al-Siddiq (may Allah be pleased with him) said: "You have taken these verses to a very harsh and difficult meaning. In reality, 'those who believe and do not mix their faith with wrongdoing' means those who did not taint their faith with shirk (associating partners with Allah), and 'those who have said, "Our Lord is Allah," and then remained steadfast' means those who acknowledged the oneness of Allah and then remained so firm upon it that they did not deviate from the truth by inclining towards shirk or any other misguidance."
Imam Ishaq bin Rahwayh recorded this report in his Musnad, and although there is criticism of its chain, its meaning is supported by other sahih hadiths and athar.