Sahih Muslim Book 9, Hadith Number 3574.

Chapter: Li’an (Invoking curse).

Abu Huraira (Allah be pleased with him) reported: There came a person to the Holy Prophet (may peace he upon him)) from Banu Fazara and said: My wife has given birth to a child who is black, whereupon Allah’s Apostle (may peace be upon him) said: Have you any camels? He said: Yes. He again said: What is this colour? He said: They are red. He said: Is there a dusky one among them? He said: Yes, there are dusky ones among them He said: How has it come about? He said: It is perhaps the strain to which it has reverted, whereupon he (the Holy Prophet) said: It is perhaps the strain to which he (the child) has reverted.