In plain words
To love with attachment to the Ātma, not to the body, is true Prema
Śaṅkara taught such an Advaita doctrine, from childhood to youth and from youth to the old, as one and the same feeling of the one Ātma. In this way the Advaita doctrine went on growing day by day. Everyone went on accepting it. At that time his guru came to Kāśī. In the past he used to call him, ‘Śaṅkara!’ Before that, a certain impurity had befallen Śaṅkara. He argued with every paṇḍita and went on bringing them into the Advaita doctrine. On that course he went to argue with a paṇḍita called Maṇḍanamiśra. That paṇḍita's wife was Ubhayabhāratī. She was a great Vedāntin. Her husband was defeated. He insisted that, by the agreement, he must take sannyāsa. Then Ubhayabhāratī: ‘Śaṅkara! You know all the Dharmas. I am his ardhāṅginī. Half of that body is I. Only when you defeat me too can he take sannyāsa. Otherwise he is not fit to take sannyāsa,’ she said. ‘Very well, begin the debate,’ said Śaṅkara. She put a question on the Kāmaśāstra, which belongs to the Dharma of the householder. Since Śaṅkara had taken sannyāsa as a child, he did not know the answer to that question. Then he took a month's time from Ubhayabhāratī. ‘I need a month to answer your question,’ he said. He set off on his way. At that time the king of Kāśī died. They laid the body of the king of Kāśī in a certain place. Seeing that this was the moment, Śaṅkara performed parakāya praveśa and entered that body. Śaṅkara's body died. He entered the king's body. The people rejoiced that the king was alive and took him into the royal palace. The one moving about in that body there was Śaṅkara himself! He entered into the householder's āśrama in which the king had lived. But his conscience would not agree to live the family life of a householder. At once he left the king's body, came back and joined his own body, and gave Ubhayabhāratī her answer. Having answered her in this way, he set out for Kashmir.