It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that a Jew came to the Prophet (peace and blessings be upon him) and said: Your nation is a good nation, if only they did not set up equals (with Allah). He (peace and blessings be upon him) said: "How do they set up equals?" He said: They say: 'Whatever Allah wills and you will.' He (peace and blessings be upon him) said: "He is saying something; (its correction is that) you should say: 'Whatever Allah wills, then whatever you will.'"
He also said: Your nation is a good nation, if only they did not commit shirk. He (peace and blessings be upon him) said: "What do they say?" He said: They say: 'By the right of so-and-so,' and 'By the life of so-and-so.' The Prophet (peace and blessings be upon him) said: "Whoever must swear an oath, let him swear only by Allah."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10430