Allons-y

You may be looking for the Doctor Who Confidential episode.

Allons-y, according to the Tenth Doctor, was French for "Let's go". (TV: Midnight) It was one of the Tenth Doctor's favourite sayings; he especially wanted to say, "Allons-y, Alonso", (TV: Army of Ghosts) which he eventually said to Alonso Frame. (TV: Voyage of the Damned) The Twelfth Doctor once claimed that he was able to say it due to his precise control over the TARDIS translation circuits. (COMIC: Four Doctors)

It saved his life on Midnight by proving that the being possessing Sky Silvestry had stolen his words. (TV: Midnight)

The Tenth Doctor yelled the phrase as he, along with twelve other incarnations, combined the power of their TARDISes to use a stasis cube to freeze Gallifrey in a pocket universe. This, combined with the Eleventh Doctor's "geronimo!", came to the irritation of the War Doctor. (TV: The Day of the Doctor)

The Doctor described it to Addams as a word of consolation to the soul in times of need. (TV: The End of Time) He was last heard using it during his final reward, as he proceeded to flee from the Gentlemen of the Dice with George Litefoot. (AUDIO: The Jago & Litefoot Revival)

Mr Clever once used it when mimicking the Tenth Doctor through the Eleventh Doctor's body. (TV: Nightmare in Silver)

In April 2004, Neil Redmond used the phrase. (AUDIO: Uncanny Valley)

The Thirteenth Doctor uttered the phrase when working with the Corsair and Team TARDIS to open a door with one hundred handholds. (COMIC: Old Friends)