(25) باب الرَّجُلُ يُهِلُّ بِالْحَجِّ ثُمَّ يَجْعَلُهَا عُمْرَةً
Abu Dharr used to say about a person who makes the intention of Hajj but he repeal it for the 'Umrah (that will not be valid). This cancellation of hajj for 'Umrah was specially meant for the people who accompanied the Apostle of Allaah(ﷺ).
Reference: Sunan Abi Dawud 1807
In-book reference: Book 11, Hadith 87
English translation: Book 10, Hadith 1803