Authentic
Sunan an-Nasa'i 3773
"You are setting up rivals (to Allah) and associating others (with Him). You say: 'Whatever Allah wills and you will,' and you say: 'By the Ka'bah.'" So the Prophet commanded them, if they wanted to swear an oath, to say: "By the Lord of the Ka'bah;" and to say: "Whatever Allah wills, then what you…
إِذَا أَرَادُوا أَنْ يَحْلِفُوا أَنْ يَقُولُوا " وَرَبِّ الْكَعْبَةِ " . وَيَقُولُونَ " مَا شَاءَ اللَّهُ ثُمَّ شِئْتَ "