During what seige did Lincoln tell Grant Hold on with a bulldog grip and chew and choke as much as possible?

President Lincoln advised Ulysses Grant to "hold on with a bull-dog grip, and chew and choke, as much as possible" during the Siege of Petersburg or as it's also known, the Richmond-Petersburg Campaign.

The chief goal of what became a brutal and very protracted campaign was to cut off Confederate General Robert E. Lee's supply lines, which Grant's army finally succeeded in doing in March, 1865.

The siege lasted approximately nine months and may be viewed as the final, fatal blow to the Confederate army. The war ended soon after, on April 9, 1865 when Lee surrendered to Grant at the Court House in Appomattox, VA.