When the Verse:-- 'Those who believe and mix not their belief with wrong." was revealed, the companions of the Prophet (ﷺ) said, "Who amongst us has not mixed his belief with wrong?" Then Allah revealed: "Join none in worship with Allah, Verily joining others in worship with Allah is a great wrong indeed."
Sahih al-Bukhari Book 60, Hadith 99
← Previous Hadith Allah's Messenger (ﷺ) said, "My example and the example o the people is like that of a person who lit a fire and let the moths, butterflies and these insects fall in it." He also said, "There were two women, each of whom had a child with her. A wolf came and took away the child of one of them, whereupon the other said, 'It has taken your child.' The first said, 'But it has taken your child.' So they both carried the case before David who judged that the living child be given to the elder lady. So both of them went to Solomon bin David and informed him (of the case). He said, 'Bring me a knife so as to cut the child into two pieces and distribute it between them.' The younger lady said, 'May Allah be merciful to you! Don't do that, for it is her (i.e. the other lady's) child.' So he gave the child to the younger lady."

Sahih al-Bukhari Book 60, Hadith 98 Next Hadith → When the Verse:-- 'Those who believe and mix not their belief with wrong.' was revealed, the Muslims felt it very hard on them and said, "O Allah's Messenger (ﷺ)! Who amongst us does not do wrong to himself?" He replied, "The Verse does not mean this. But that (wrong) means to associate others in worship to Allah: Don't you listen to what Luqman said to his son when he was advising him," O my son! Join not others in worship with Allah. Verily joining others in worship with Allah is a great wrong indeed." (31.13)

Sahih al-Bukhari Book 60, Hadith 100