No, not about being unable to provide for offspring, I think in this case the situation is that the adopting individual don't have their own kids and he has showed desire to adopt someone they know who's been blessed with blessing of children.
Assalamu Alaikum,
Can somebody provide fewa regarding; if it is permisable to give your own child to your brother away?
Assalamu Aleykum
It's permissible, Insha'Allah, as long as you are sure the brother you are giving to will act like his guardian and you (or whoever is the subject) will be considered the real parent. Allah Azwajal, in Quran, says:
“…nor has He made your adopted sons your real sons…”
[33:4]
Before you take this major step, please make sure that person is going to be kind to your child in future, he'll give him good Islamic upbringing and will teach him Deen, and so forth. Best wishes! May Allah reward you for your good deed.
The most relative fatwa I've been able to find:
http://www.islam-qa.com/en/ref/10010/adoptation child