Clarke's Law

Clarke's Law stated, "Any sufficiently advanced form of technology is indistinguishable from magic." (TV: Battlefield)

The Captain paraphrased this by explaining that his now-wrecked craft had possessed technologies "indistinguishable from magic." (TV: The Pirate Planet)

The Seventh Doctor reminded Ace of Clarke's Law and stated that "the reverse is true", as was the case of the Thirteen Worlds, a parallel universe where technology formed alongside magic. (TV: Battlefield)

When asked by the Tenth Doctor on how the Sisters of Plenitude cured Petrifold Regression, Matron Casp responded "primitive species would accuse us of magic, bit it's merely the tender application of science". (TV: New Earth)

When Angelo Colasanto believed Captain Jack Harkness' vortex manipulator to be magic, Jack corrected him saying it was technology, although the two could be indistinguishable. (TV: Immortal Sins)

The Twelfth Doctor paraphrased the law to Clara Oswald when stating how he would impress a Viking village with a Yo-yo. (TV: The Girl Who Died)

The Thirteenth Doctor quoted the law to King James I. (TV: The Witchfinders)

Behind the scenes
In the real world, this is actually Arthur C. Clarke's Third Law.