Dattatreya Avatar
The three Goddesses, Lakshmi, Parvati and Saraswati were very proud of their Pativrata nature. Lord Vishnu then planned a scheme to kill their pride. As per Lord Vishnu's plan, Narad went to all three of them separately and told them that Atri's wife Anusuiya's pativrata nature is even bigger than theirs. All three devi's went up to their respective husbands and asked them to take a test of Anusuiya's pativrata.
Following their wives order, Lord Shiva, Vishnu and Brahma went to the ashram of Atri in disguise of sage. At that time Maharshi Atri was not in his ashram. All three of them asked for bhiksha from Anusuiya, but the condition was to give them the bhiksha without wearing any clothes.
Anusuiya was shocked to hear their condition, but later she decided not to insult the sadhu's and said, if my love for my husband is true, while giving them bhiksha, all these three sadhus should turn into 3 month-old babies.
Instantly all three Gods turned into babies and started crying. Then Anusuiya took Devi Ma's form and took all three of them in her arms and breast fed them and put them in swings. When the three gods didn't return on time, their wives got worried. Narad then told them the entire story. Listening to the story, all three Goddesses went to Anusuiya and asked for forgiveness.
It was then when Anusuiya changed the three Gods back into their original form. The three Gods blessed Anusuiya that they will fill her womb with a baby made of all three of their bodies. Then from Brahma's ansh Chandrama, Shiva's ansh Durvasa and from Vishnu's ansh Dattatreya was born.