Read Defense Secretary Jim Mattis' Farewell Message

Retired Gen. Jim Mattis, the outgoing Secretary of Defense, told staff at the Department of Defense to “keep the faith in our country” in a farewell message sent on Monday.

The short letter came on Mattis’ last day as Secretary of Defense, after he was forced out of the post following a clash with President Donald Trump over the decision to withdraw U.S. troops from Syria.

The full letter reads:

On February 1, 1865, President Lincoln sent to General Ulysses S. Grant a one sentence telegram. It read: “Let nothing which is transpiring, change, hinder, or delay your military movements, or plans.”

Our Department’s leadership, civilian and military, remains in the best possible hands. I am confident that each of you remains undistracted from our sworn mission to support and defend the Constitution while protecting our way of life. Our Department is proven to be at its best when the times are most difficult. So keep the faith in our country and hold fast, alongside our allies, aligned against our foes.

It has been my high honor to serve at your side. May God hold you safe on the air, on land, and at sea.

One day after President Trump unexpectedly announced U.S. troops would be withdrawn from Syria, Mattis announced he would be resigning.

His resignation letter was seen as a rebuke of Trump’s military policy, including his rhetorical attacks on NATO and other longtime U.S. allies. It ended with, “you have a right to have a Secretary of Defense whose views are better aligned with yours.”

Mattis was originally meant to leave his post at the end of February, in an effort to ensure a smooth handoff of control of the Pentagon. However, on Dec. 23, Trump abruptly moved Mattis’ resignation date forward to Jan. 1, 2019.

Mattis is scheduled to transfer responsibility to his deputy, Patrick Shanahan, on Monday evening.

Write to Billy Perrigo at billy.perrigo@time.com.