The conditions of the one criticising and one being praised

There are four opinions:

1. According to Imām Abū Ḥanīfah and Imām Abū Yūsuf, may Allāh ﷻ have mercy upon them, jarḥ and ta’dīl are the same as khabr. Thus, there is no stipulation in terms of number of narrations, for the narrator to be a free-man,[1] nor for the narrator to be male. Thus, the jarḥ and ta’dīl of a single ādil narrator will be accepted, regardless of whether he is a free-man or a slave, male or female. This is the view which is muftā bihī[2] according to the Ḥanafi scholars.
2. According to Imām Muḥammad and Imām Ṭaḥāwī, jarḥ and ta’dīl are the same as testimonies. Therefore, the stipulations made for testimony with regards to the number of narrators, being a free-man and being male also hold for jarḥ and ta’dīl. Thus jarḥ and ta’dīl is not accepted from one narrator, nor is it accepted from a slave or a woman. This is also the view which has been strengthened by al-Bāqilānī to many of the fuqaḥā of Madīnah as well as others.
3. According to the majority of the uṣūliyyīn, conditions are dependent on the thing being stipulated. Therefore, with regards to the jarḥ and ta’dīl of narrators, there is no stipulation of number of narrators, nor being free or male. This is because when relating a narration these conditions are not found. Nor do they add conditions such as establishment of adālah in order to accept the narration, and nor are any conditions removed. As for jarḥ and ta’dīl of testimonies, number and being free are stipulated, as these are conditions found when accepting a testimony. As for being a male, this is not a condition in rulings where the testimony of one woman is sufficient,[3] but it is a condition for cases other than this.
4. Al-Sam’ānī has given strength to the majority of fuqaḥā and muḥaddithīn: the ta’dīl of narrators is the same as khabr, thus there are no conditions with regards to this, and the jarḥ of narrators is the same as testimonies, thus the conditions for testimonies hold for jarḥ. 

From these four opinions, three are widespread, with the last opinion being less famous. 

Thereafter, there is an additional condition that the one doing jarḥ and ta’dīl should be known to be ādil and unbiased.

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[1] And not a slave

[2] Fatwā is given upon

[3] Such as giving birth.