Read the whole article yourself: http://www.masud.co.uk/ISLAM/nuh/evolve.htm
Here's my summary:
1) Proof that Moulana Shaykul Islam Kellar (God Bless him) believes in Micro-evolution (minor alterations in a species that do not mutate it into another species):
"micro-evolution within a species ... is fairly well-attested to by breeding horses, pigeons, useful plant hybrids, and so on"
2) non-human macro-evolution: Shaykh Kellar also does not deny the possibility of non-human macro-evolution (the alteration of an non-human species to such an extent that it becomes a new non-human species). He believes that non-human macro-evolution in animals does not contradict the Islamic creed and that someone who believes in non-human macro-evolution is not committing kufr.
3) Ape-Human macro-evolution: Belief in Ape-human macro-evolution is Kufr. Ape-human macro-evolution is the belief that a hairy, buck-teethed monster with a propensity to pick its nose and eat its poo could mutate into an intelligent human.
I believe that our non-accpetance of category 3 evolution is because of the Quranic verse Inna khalaqnal insaana min nutfatin....
Finally, Shaykhuna Keller says that belief in non-human micro and macro-evolution must be predicated in the understanding that the ultimate cause of all these 'mutations' is Allah.