There’s no saying exactly like it in the Pali suttas and most of the modern writers who quote it don’t state from whence it came. The few who give a citation say that it’s section XXIV of the Sūtra in Forty-two Sections.
However, whether this is what the original Chinese says, I’ve no idea. Of the translations I’ve looked at, six are supportive of the attribution and three are not.
The supportive ones are Ricius’s Latin rendering:
Evigilatus ait: Speciei nulla major est appetentia nullum enim magis appetendum quam species usquam datur. Feliciter haec una est, quodsi duae essent, nemo terrigenarum viae se exercere valeret.
And the English ones by Heng-Ching Shih:
The Buddha said, “Of all desires, there is none worse than lust. Of desires, lust has no equal. Fortunately, it is one of a kind. If there were another desire so strong, no one in the world could follow the Way.”
Buddha said: Of all the sensual passion [sic] there is none so powerful as sexual inclination. It is so strong that there is no other worth comparing to it. But most happy [sic], there is but one passion of this description; for, if there were two, not one man in the whole world would be able to follow the precepts of truth.
Buddha said: Of all the passions (lit., lusts and desires) the greatest is love of women. Besides this, - so great is it, - there is no other. Were there two of the same sort, no mortal would be able to attain supreme reason.
Chung Tai Translation Committee:
The Buddha said, “There is no desire more powerful than sex; sex as a desire has no equal. Fortunately, there is no other like it. If there were, no one in the world would be able to cultivate the Way.”
Master Hsuan Hua and disciples:
The Buddha said, of all longings and desires, there is none as strong as sex. Sexual desire has no equal. Fortunately, it is one of a kind. If there were something else like it, no one in the entire world would be able to cultivate the Way. "
The unsupportive ones are those of Soyen Shaku and D.T. Suzuki:
The Buddha said: “There is nothing like lust. Lust may be said to be the most powerful passion. Fortunately, we have but one thing which is more powerful. If the thirst for truth were weaker than passion, how many of us in the world would be able to follow the way of righteous?”
The Buddha said: "Of all longings and desires, there is none stronger than sex. Sex as a desire has no equal. Rely on the (universal) Oneness. No one under heaven is able to become a follower of the Way if he accepts dualism.
And Karl Seidenstücker:
Der Buddha sprach: “Es gibt nichts, was der Lust gleich wäre. Die Lust kann als die mächtigste Leidenschaft betrachtet werden. Glücklicherweise besitzen wir noch eine Eigenschaft, welche mächtiger ist. Wäre der Durst nach Wahrheit schwächer als die Leidenschaft, - wie viele von uns in der Welt würden fähig sein, dem Pfad der Gerechtigheit zu folgen?”