In the place, with an example.

The Shaykh : In the place: A man performs i'tikaf (spiritual retreat) in his home instead of performing it in the mosque. We say that this i'tikaf is not valid because it did not conform to the Shari'ah regarding the place, for the place of i'tikaf is the mosques, whether it is the Sacred Mosque, the Prophet's Mosque, the Al-Aqsa Mosque, the congregational mosque in other countries, or the mosque where the congregation is held in other countries. The important thing, may Allah reward you, is that you should know that worship does not conform to the Shari'ah unless it conforms to the Shari'ah in these six matters.