Sunan Ibn Majah, Hadith 2118 ⓘ

It was narrated from Hudhaifah bin Yaman that : a Muslim man saw in a dream that he met a man from among the People of the Book, who said: "What good people you would be if only you were not committing Shirk. For you say: 'What Allah wills and Muhammad wills."' He mentioned that to the Prophet and he said: "By Allah, I am aware of that. Say: 'What Allah wills then what Muhammad wills."'Another chain from Tufail bin Sakhbarah, the brother of 'Aishah by her mother, from the Prophet, with similar wording.

حَدَّثَنَا هِشَامُ بْنُ عَمَّارٍ، حَدَّثَنَا سُفْيَانُ بْنُ عُيَيْنَةَ، عَنْ عَبْدِ الْمَلِكِ بْنِ عُمَيْرٍ، عَنْ رِبْعِيِّ بْنِ حِرَاشٍ، عَنْ حُذَيْفَةَ بْنِ الْيَمَانِ، أَنَّ رَجُلاً، مِنَ الْمُسْلِمِينَ رَأَى فِي النَّوْمِ أَنَّهُ لَقِيَ رَجُلاً مِنْ أَهْلِ الْكِتَابِ فَقَالَ نِعْمَ الْقَوْمُ أَنْتُمْ لَوْلاَ أَنَّكُمْ تُشْرِكُونَ تَقُولُونَ مَا شَاءَ اللَّهُ وَشَاءَ مُحَمَّدٌ ‏.‏ وَذَكَرَ ذَلِكَ لِلنَّبِيِّ ـ صلى الله عليه وسلم ـ فَقَالَ ‏ "‏ أَمَا وَاللَّهِ إِنْ كُنْتُ لأَعْرِفُهَا لَكُمْ قُولُوا مَا شَاءَ اللَّهُ ثُمَّ شَاءَ مُحَمَّدٌ ‏" ‏ ‏.‏