If Someone Has Become Known for Lying - Do not be sympathetic because of some of his good deeds
Sometimes it so happens that a person becomes known as a liar, because of clear lies he tells. When this is the case, you find some people who refuse to recognize him as a liar, defending him, claiming that he is very pious, basing their position on his open acts of obedience.
The following quote should show us how a liar may very well be concealing his inner filth with beautiful drapery of outward obedience and piety.
As-Suyootee said in Tadreed ar-Raawee (in Term #21: al-Mowdhoo', 1/333-334 of the Kowthar 2nd printing, 1415):
Ghulaam Khaleel used to be abstinent and shun worldly pleasures, and the marketplaces of Baghdaad all closed for his funeral (meaning: he was so popular in a place focused on religious piety). Even with this, he used to fabricate hadeeth [...] saying (at the time of his death), "I have invented 70 hadeeth about the virtues of 'Alee!"
And Aboo Daawood an-Nakha'ee used to stand in prayer at night longer than anyone else and fast more than anyone, yet he used to fabricate (narrations on the Prophet sallallaahu alayhe wa sallam).
And Ibn Hib-baan said: Aboo Bishr Ahmad ibn Muhammad al-Faqeeh al-Marwazee was from the firmest of the people of his time upon the Sunnah, and he was the most active in defending it, and the most brutal in dealing with those who opposed it. All of this, while he used to fabricate narrations!
And Ibn 'Adiyy said: Wahb ibn Hafs was one of the righteous (openly), he even spent twenty years not speaking to anyone (perhaps fearing the harvest of his bad statements, perhaps because of a soofee "vow of silence"), and with all this he used to tell audacious lies!
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Our salaf used to refrain from mentioning the good deeds of the people of innovation, and say things like: Praising a person of innovation aids in the destruction of Islaam. (attributed to al-Fudhayl ibn 'Iyyaadh and others)
We do not deny their good deeds either. That is simply unjust.
An example of how we might interact with the mention of the good deeds of a specific person from the innovated sects:
A soofee who feeds the poor people and aids them with social services... We might hear about his deeds and ask Allaah (privately) to accept them and guide him by way of them. We might even say to ourselves: If a soofee is doing this, what am I doing? and thus gain some benefit from hearing about his good deeds. But we would not mention them publicly, fearing that we would give "good press" to the people of innovation, and thus guide people to them and their way.
Our shaykh Rabee' ibn Haadee al-Madkhalee (may Allaah preserve him) said in response to occasions when some of the Muslim biographers mentioned the good deeds of some of the people of innovation,
"This (public mention of their good deeds) has never aided Islaam!"
And Allaah knows best.
Moosaa ibn John Richardson