Lord Dattatreya is the incarnation of Brahma, Vishnu and Shiva.
Sage Narada praised Anusuya's "pativratyam" (Devotion to her husband) a lot before the wives of Brahma-Vishnu-Shiva making them jealous of her. They requested their husbands to reduce her pativratyam. Brahma, Vishnu and Shiva went to Anusuya as guests when Atri was not there at home and asked her to serve them food. When she agreed to do so, they said that they will accept her alms on the condition that she serves them without wearing clothes. Anasuya falls into a dilemma. If she comes without clothes in front of other men her pativratyam will be reduced. If she refuses then that is dishonour to the guests and they can take away all the power of Atri. Anasuya felt that the three guests who asked such a strange favor are not normal people since they are trying to place her in a tricky situation. Anasuya prayed to her husband in her mind and said that she doesn't have any fear serving them without clothes as she is not affected by lust. Since the guests asked for alms saying "Bhavati Bhiksham Dehi" (Oh Mother! Give us some food) and indirectly called her a mother. She decided that she will consider them as her children and serve them as requested. Because of her greatness and as per her thinking by the time she came to serve food the three gods became small children and her breasts started producing milk. She then breastfed them and put them to sleep in a cradle. Atri came back afterwards and hearing the story from Anasusuya praised the three gods sleeping in the cradle. They woke up in their original form and praised Anasuya's pativratyam and gave her a boon. Anasuya requested that these three should be born as her children the incarnation of Shiva, Vishnu and Brahma as sage Durvasa, Dattareya and the moon-god Chandra.
