Layla bint Harmalah
- I have taught you the Qur'an, clarified to you arguments, apprised you of what you were ignorant and made you swallow what you were spitting out. Even a blind man would have been able to see, and he who was sleeping would have been awakened. How ignorant of God is their leader Muawiyah and their instructor Ibn an-Nabighah.
"Al-Nabighah" is the nickname of the mother of Amr ibn al-A'as according to many Shias. He is called "son of his mother" because of his mother's reputation: once Arwa bint al-Harith went to Muawiyah and during their conversation Amr ibn al-A'as intervened. Arwa said to Amr:
"O son of al-Nabighah, you too dare speak, although your mother was known publicly and was a singer of Mecca? That is why five people claimed you (as a son), and when she was asked she admitted that five people had visited her and that you should be regarded as the son of him you resembled most. You must have resembled A'as ibn Wa'il and therefore you came to be known as his son." These five persons were:
A'as ibn Wa'il Abu Lahab Umayah ibn Khalaf Hisham ibn al-Mughirah Abu Sufyan ibn Harb 
This is probably the first ever instance of the manifestation of the doctrine of "Takfir". Calling a Muslim men Kafir is a great sin in Islam.
Sunnis tend to stay away from criticizing the Sahabah and their relatives, even though some Sahabah were known to wage war with each other shortly after the death of Muhammad. Furthermore, Sunnis maintain that slandering anyone is an unjust act, pointing to the Quranic verse 4:15
"If any of your women are guilty of lewdness, Take the evidence of four (Reliable) witnesses from amongst you against them; and if they testify, confine them to houses until death do claim them, or Allah ordain for them some (other) way."
And they maintain that because there wasn't four eye-witnesses of Layla having commit adultery as is alleged, that it is unjust to simply believe in some unsubstantiated rumors. No Sahih Sunni hadiths mention these allegations against Layla. However, it is also possible that the five visited her separately and it was not a Nikah Ijtimah.