Wrongful accusation is the worst possible crime.
Say: "Come, I will tell you what your Lord has made binding on you: that you ascribe no partner unto Him: that you show kindness to your parents; that you slay not your children because of poverty; We provide for you and for them; that you commit not any shameful deeds, openly or secretly; that you slay not the soul God has prohibited except by right. Thus God exhorts you, that you may grow in wisdom. Do not touch the property of orphans, but strive to improve their lot until they reach maturity. Give just weight and full measure; We never charge a soul with more than it can bear. When you speak, be just, even though it be against a relative. Be true to God's covenant. Thus God exhorts you, so that you may take heed.
(6: 151-152)
Say: "My Lord has forbidden only shameful deeds, whether outward or inward, and sin and wrongful oppression; and that you associate with God that for which no warrant has been revealed, or to tell of God what you do not know. Every nation has its term; when their hour comes they shall not put it back by a single hour nor put it forward. Children of Adam, when apostles of your own come to proclaim to you My revelations, those that take warning and mend their ways will have nothing to fear or to regret; but those that deny and scorn Our revelations shall be inhabitants of the Fire, and there they shall remain forever.
(7:33-36)