It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) in a marfu’ form that whoever says "Insha’Allah" while eating, then he has the choice: if he wishes to fulfill his oath, he may do so, and if he wishes to retract from it, he may do so without becoming a violator of his oath.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 6103