And Allah the Almighty says:

“{..and your [foster] mothers who suckled you.}” (An-Nisa' 23).

And it is not permissible for a person to let his brother or his nephew hear [the knowledge].

It is not permissible for the "nursed" disciple (al-tilmidh al-murda’), if he forgets, to hear [the knowledge] from the disciple of his foster-father (murdi’), for he is his brother through "fosterage" (radha’ah).

It is not permissible for a believer to let a son hear [the knowledge] and then let the father of that son hear it, for he is [in the position] of the mothers of [one's] wives.

It is not permissible for a believer to let the biological son of his disciple hear [it]; rather, it is permissible for the disciple to let the biological son of his master (sayyid) hear [it].

A master may not let the disciple of his biological son hear [the knowledge], unless he has no [spiritual] connection (ta’liqah) over his biological son, according to the saying of the Almighty: “{...and [forbidden to you are] the wives of your sons who are from your [own] loins.}” (An-Nisa' 23).

It is not permissible for a person to let two individuals who are biological brothers hear [the knowledge together];