The short answer
No. The phrase is not in The Wealth of Nations, not in The Theory of Moral Sentiments, and not in the lecture notes his students copied out. It is French, and older than he was.
Where it came from
The Marquis d'Argenson, a minister of Louis XV, was using it in his diary by 1736, and in 1751 printed the story of its origin: around 1681 the finance minister Colbert asked a merchant named Le Gendre what the state could do for trade, and Le Gendre answered, leave it to us. Others stretched it to laissez faire et laissez passer, and the French économistes took it up.
Smith spent ten months among those économistes in Paris and never wrote the phrase down.
What he said instead
His own phrase was English and plainer: the system of natural liberty. And in the same book that describes it, he wanted the banks regulated, defended the Navigation Act as perhaps the wisest of England's commercial regulations, and thought it reasonable that the rich pay more than their share of tax.
What he did write, in 1755, was leave her alone. The her was nature, and the man told to leave her alone was the statesman who imagined he could arrange a society like a machine. It was not a merchant asking a minister for a free hand.