What is the ruling on a husband having intercourse with his wife on the twelfth day after her childbirth, after she had become pure and seen pink blood and water after the first intercourse which then stopped, and then blood and water reappeared after the second intercourse? Is expiation (kaffarah) obligatory, and upon whom is it obligatory? And what is the ruling on prayer and fasting after this blood?

There is no minimum limit for lochia (postnatal bleeding). Whenever a woman sees purity, she must perform ghusl (ritual bath) and pray, and intercourse becomes permissible for her, even if it is before the forty-day mark. The first instance of intercourse is not sinful, but ghusl should have been redone after seeing the returning blood, as the returning blood is considered lochia. The acts of worship performed before the return of the blood are valid because the intermittent purity is a valid purity. Your husband was not permitted to have intercourse with you before you performed ghusl from the returning blood, but no expiation is required. If you delayed ghusl or prayed without performing ghusl from the returning blood, you must make up those prayers.