When they lost all hope in him, they spoke privately. The eldest of them said, “Do you not know that your father had taken a Solemn oath by Allah from you, nor how you failed him regarding Yusuf before? So I am not leaving this land until my father allows me to, or Allah decides for me. For He is the Best of Judges.
Meaning:-
Solemn: sincere, earnest, honest, genuine, firm,
oath: a formal and very serious promise.