Sayyiduna Ibn Umar (may Allah be pleased with them both) narrates that Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) said: O Messenger of Allah! In the Days of Ignorance I vowed that I would perform i'tikaf for one night in al-Masjid al-Haram. He (peace and blessings be upon him) said: "Fulfil your vow."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8586
Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrates that the Prophet (peace and blessings be upon him) said: "Fasting is not obligatory upon the mu'takif unless he makes it obligatory upon himself."
Abdullah bin Muhammad bin Nasr al-Ramli alone narrated it. The correct version is mawquf (a saying of Ibn Abbas), and attributing it to the Prophet (peace and blessings be upon him) is an error.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8587
Amr bin Zurarah narrates that Abd al-Aziz narrated to us the same report as a brief mawquf hadith; and so Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) did not consider fasting obligatory upon the mu'takif.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8588