Musannaf Ibn Abi Shayba 33:784

Waki’ narrated to us, he said: Al-A’mash narrated to us, from Mujahid, he said: I heard him narrating from ‘Ubayd ibn ‘Umayr al-Laythi: That when the flood afflicted the people of Nuh, he said: And there was a woman with him who had a young child with her. He said: So she lifted him up to her waist. When the water reached it, she lifted him up to her chest. When the water reached it, she lifted him up to her breasts. Allah said: "If I were to have mercy on anyone among them, I would have had mercy on her," meaning because of her mercy for the child.