Musannaf Ibn Abi Shayba 27:473

Yahya ibn Ya'la narrated to us, from Yunus ibn Khabbab, from Anas, who said: I went out with Ali along with the Messenger of Allah (peace and blessings of Allah be upon him) into a garden of Medina. We passed by a garden, and Ali said, "How beautiful this garden is, O Messenger of Allah!" The Messenger of Allah (peace and blessings of Allah be upon him) said, "Your garden in Paradise is more beautiful than this, O Ali." He continued until he passed by seven gardens. Each time, Ali would say, "How beautiful this garden is, O Messenger of Allah!" and he would reply, "Your garden in Paradise is more beautiful than this."