In The Name of Allah, The Most Merciful, The Bestower of Mercy.

Imam Al-Khatib Al-Baghdadi, may Allah have mercy upon him, said:

There is no one among the people of hadith who showed favoritism (or behaved in a biased manner) in hadith — neither toward his father, his brother, nor his son. Ali ibn Abdillah Al-Madini, may Allah have mercy upon him, was an Imam of hadith in his era, however, not a letter is reported from him with regards to strengthening (the reliability of) his father; rather, the opposite of that is what has been narrated from him. [1]

Imam Ibn Hibban, may Allah have mercy upon him, said: “Ali Ibn Al-Madini, may Allah have mercy upon him, was asked about his father, so he said: ‘Ask someone else’. They said: ‘We ask you (in particular)’. He lowered his head (in silence for a while), then he raised his head and said: “This is the religion, my father is weak (in hadith)”. [2]

[1] Sharaf Ashab al-Hadith p. 41
[2] Al-Majruhin 2/15