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One day after President Trump unexpectedly announced U.S. troops would be withdrawn from Syria, Mattis announced he would be resigning.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

Get our Politics Newsletter. The headlines out of Washington never seem to slow. Subscribe to The D.C. Brief to make sense of what matters most. Please enter a valid email address. Sign Up Now Check the box if you do not wish to receive promotional offers via email from TIME. You can unsubscribe at any time. By signing up you are agreeing to our Terms of Use and Privacy Policy . This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply. Thank you! For your security, we've sent a confirmation email to the address you entered. Click the link to confirm your subscription and begin receiving our newsletters. If you don't get the confirmation within 10 minutes, please check your spam folder.

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