Hadith.4290 - Al-Halabi said: I asked Imam (as) about a man who makes a vow upon himself without specifying it.
Imam (as) said: "If you specify it, then it is as you specified. But if you do not specify anything, then it is of no consequence. However, if you said: 'It is upon me for the sake of Allah (swt),' then its expiation is the expiation of an oath."