This image is of a Phurba, a ritual dagger used in rites of subjugation of hostile forces, associated with certain cycles of tantric teachings. Its three edges symbolise cutting through the three main disturbing emotions of ignorance, anger and attachment. It was made in Tibet in the 13th or 14th century. Its handle is carved from wood and painted, with gilding and ivory details. Further details can be seen here.
It is currently on display at the Ashmolean Museum of Art and Archaeology in Oxford, which has recently re-opened after conducting a major face lift over the last five years. The Himalayan and Tibetan section is expanded with numerous objects on display (mostly sculpture) along with three paintings, one of the Mandala of Guhyasamaja-Manjuvajra and two, in the Karma Gardri style, of the 8th Situpa Panchen Chökyi Jungne (1700-74), here and here.
If you’re in Oxford or passing by, it’s definitely worth checking out.