Is the phrase "By God, it's the last..."—which was left incomplete—considered a slip of the tongue (laghw) or an oath (yamin)?

Whoever begins an oath but does not complete it is not bound by the oath, nor is it constituted, unless he intended to suffice with what he had uttered. So, if his intention was to complete the oath but he did not do so, there is nothing upon him. However, if he intended to suffice with what he had uttered, the oath is constituted, and expiation becomes binding upon him if he breaks it.