It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that Sayyiduna Umar (may Allah be pleased with him) used to swear by saying «وابي». The Prophet Muhammad (peace and blessings be upon him) forbade him from this and said: "Whoever swears by other than Allah has committed shirk (associating partners with Allah)."
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 4904
Hadith Gradingحکم دارالسلام:رجاله ثقات إلا أن سعد بن عبيدة لم يسمع هذا الحديث من ابن عمر مباشرة.