… is from page 333 of the 1982 Liberty Fund issue of the 1978 Oxford University Press edition of Adam Smith‘s Lectures on Jurisprudence (available on-line here); specifically, this quotation is from Smith’s lecture of March 28, 1763 (footnote and annotations deleted):
Upon the whole it is the custom of having many retainers and dependents which is the great source of all the disorders and confusion in some cities; and we may also affirm that it is not so much the regulations of the police which preserves the security of a nation as the custom of having in it as few servants and dependents as possible. Nothing tends so much to corrupt and enervate and debase the mind as dependency, and nothing gives such noble and generous notions of probity as freedom and independency. Commerce is one great preventive of this custom. The manufactures give the poorer sort better wages than any master can afford; besides, it gives the rich an opportunity of spending their fortunes with fewer servants, which they never fail of embracing. Hence it is that the common people of England who are alltogether free and independent are the honestest of their rank any where to be met with.
Commerce – a natural result of wide scope for capitalist acts among consenting adults – is the foundation of a peaceful and civilized society.