Question Summary:
Can a child carry mother’s surname?

Question Detail:

Is it permissible to give a child its mother's last name instead of the father's last name? For example, let's say the father's name is Jon Smith, he was not born or raised as a muslim but converted to Islam before marrying his wife. The wife's name is Aisha Yusuf, she was born and raised as a muslim. Would it be permissible to give their child the mother's last name, since it's more Islamic and the child may identify more as a muslim with the mother's last name instead of the father's? Example: Hasan Yusuf instead of Hasan Smith.

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
It is permissible to give the child the mother’s surname for the purpose stated in the email on condition that the intention is not to disassociate the child from the father.[1]   
And Allah Ta’āla Knows Best
Tahmid Chowdhury
Student Darul Iftaa
New York, USA
Checked and Approved by,
Mufti Ebrahim Desai.