52 JC No 3

Christian freedom

The third part of Christian freedom lies in this: regarding outward things that are of themselves 'indifferent', we are not bound before God by any religious obligation preventing us from sometimes using them and at other times not doing so, as it suits us. And the knowledge of this freedom is very necessary to us, for, if it is lacking, our consciences will have no rest and there will be no end of superstitions. Today we seem to many people to be unreasonable because we stir up discussion upon the unrestricted eating of meat, use of holidays and of vestments, and such things which seem to them vain frivolities. But these matters are more important than is commonly believed. For when consciences once ensnare themselves, they enter a long and inextricable labyrinth, without an easy exit.

If a man begins to doubt whether he may use linen for sheets, shirts, handkerchiefs, and napkins, he will afterward be uncertain also about hemp; finally, doubt will even arise over tow. For he will turn over in his mind whether he can sup without napkins, or go without a handkerchief. If any man should consider daintier

food unlawful, in the end he will not be at peace before God, when he eats either black bread or common victuals, while it occurs to him that he could sustain his body on even coarser foods. If he boggles at sweet wine, he will not with clear conscience drink even flat wine, and finally he will not dare touch water if sweeter and cleaner than other water. To sum up, he will come to the point of considering it wrong to step upon a straw across his path, as the saying goes.
Institutes 3.19 (I think I've used two different translations here)