Dr. `Ali Al-Hammadi
From "Fi Qafas al-Ittiham" 1420 Dar IbnHazm

Having A Good Opinion of People

From leading principles to which the Muslim needs to pay attention before he raises any doubt and before he accepts and believes in any accusation is to give priority to having a good opinion over having a bad opinion of his Muslim brothers. He should look for excuses and justifications that will excuse them and clear them of blame, especially when the accusation is directed towards callers to Allah and the righteous.
This is the practice of the righteous, people of understanding and wise men from among Muslims who fear their Lord and desire victory and predominance for Allah's Deen.
Had it been the other way around - had having a bad opinion of people been given a priority over having a good opinion, then no scholar would have been left without being maligned, no nobleman without faults found in him, and Muslims would be deprived from good examples. That is a methodology that is accepted neither by the Islamic Law nor by any logic.
“The basic principle in this rule is the saying of Allah `azza wa jall: “O you who have believed, avoid much [negative] assumption. Indeed, some assumption is sin. And do not spy or backbite each other. Would one of you like to eat the flesh of his brother when dead? You would detest it. And fear Allah; indeed, Allah is Accepting of repentance and Merciful.” [Al-Hujurat 49:12]
Allah `azza wa jall ordered avoiding much of the suspicion because some of it is sin, and He followed this order with the prohibition of spying, pointing out that spying in most cases does not occur except due to bad assumptions.
The way of the Muslim – the general rule - is hiding others' faults and having a good opinion of others. This is why Allah `azza wa jall ordered believers to have a good opinion of people when they hear slanders of their Muslim brothers.
And in the story of ifk (the lie which hypocrites invented against A`isha, the Mother of the Believers, from which Allah declared her free and innocent in the Quran), when it was said what was said, Allah `azza wa jall clarified the true position which every Muslim must understand. He said subhanahu wa ta`ala:
“Why, when you heard it, did not the believing men and believing women think good of themselves [i.e. one another] and say, 'This is an obvious falsehood'?” [An-Noor 24:12]” [Hisham Ismail As-Sini, Manhaj Ahl As-Sunnah wal Jama`ah fin Naqd wal Hukm `ala al Akhirin, Al Muntada, London, 1992, p. 21]

Dr. Mustafa as-Siba'i said, “Because having a good opinion and then regretting is better than having a bad opinion and then regretting.” [as-Sibai, Hakadha `allamatni al Hayat, al Maktab al Islami, Beirut, 1984, vol. 1, p. 42]