Purchase bills of non mentioned commodities in GST non core field

We have traded in an item which was non mentioned by us on the top 5 commodities in our GS profile in non core fields. The GST officer is threatening to reject the ITC claimed by us on these purchases saying we have not mentioned this item in REG-14. This item has been purchased by us for the first time & is not a regular item for future business, Kindly mention what does the GST rule say about this matter. Thank You