Sunni Sources - 1

Those people who blame Hazrat Abutalib (as) about not being a Muslim should refer to their own books.

We quote from "Al Sabta, Tameez As Sahaba" written by Allama Ibne Hajr Askalani a prominent Sunni Scholar.

1) Hazrat Abutalib (as) addresses the Holy Prophet (s.a.w.w.) as "Ya Rasool Allah (s)"

The below given extract clearly shows that Hazrat Abutalib (as) adresse the Holy Prophet (s.a.w.w.) as "Ya Rasool Allah" in one of his poems, he even goes ahead to tell that I know that the Holy Prophet (s.a.w.w.) is truthful and his religion is the best from among the religions of the world.

Now no one would address the Holy Prophet (s.a.w.w.) as "Ya Rasool Allah" other than a muslim.

2) Hazrat Abutalib (as) tells the Holy Prophet (s.a.w.w.) to pray to Allah (s.w.t.) for his health.

One day when Hazrat Abutalib (as) fell ill he requested the Holy Prophet (s.a.w.w.) to pray to Allah (s.w.t.) for his health. 

Now a muslim will never pray to false gods as he does not believe in them similarly if Hazrat Abutalib (as) did not believe in Allah (s.a.w.) then he would never had asked the Holy Prophet (s.a.w.w.) to pray to Allah (s.w.t.) to restore his health.