What is the evidence for limiting the time of i'tikaf (spiritual retreat in the mosque) to Ramadan?

The questioner : The questioner says: Honorable Shaykh, if the Prophet (peace and blessings be upon him) prayed eleven or thirteen units of the night prayer and did not exceed that, but he did not specify the number of rak'ahs (units of prayer) for the night prayer, does his i'tikaf (spiritual retreat in the mosque) in Ramadan not also imply that the time for i'tikaf is not specified? If that is not the case, where did we take the specification of the time for i'tikaf from?

The Shaykh : We took the non-specification of the number of rak'ahs for prayer from the answer of the Messenger (peace and blessings be upon him). As for i'tikaf (spiritual retreat in the mosque), the Prophet (peace and blessings be upon him) did not legislate it except in Ramadan, and he clarified that he performed i'tikaf for the sake of Laylat al-Qadr (the Night of Decree). It is known that Laylat al-Qadr does not occur in any month other than Ramadan, for Laylat al-Qadr is certainly in Ramadan, by the saying of Allah the Exalted: On Laylat al-Qadr: If we take the first and second pieces of evidence, it is established that Laylat al-Qadr is in Ramadan, and the Messenger (peace and blessings be upon him) only performed i'tikaf seeking and desiring Laylat al-Qadr.