Sunan Ibn Majah, Chapter: The Chapters on Hunting

"I said: 'O Messenger of Allah, I have come to you to ask you about the vermin of the earth. What do you say about mastigures?' He said: 'I do not eat them and I do not forbid them.' I said: 'I will eat of that which you have not forbidden. But why (do you not eat them), O Messenger of Allah?' He said: 'One of the nations was turned into beasts and I looked at this creature and was uncertain.' I said: 'O Messenger of Allah, what do you say about rabbits?' He said: 'I do not eat them and I do not forbid them.' I said: 'I will eat of that which you have not forbidden. But why (do you not eat them), O Messenger of Allah?' He said: 'I have been told that it menstruates.'"