I have investigated the source of this quote only to ascertain if it is really his not to take anything away from the quote. It may be that he said it after all, but so far I have not been able to find it sourced anywhere in his writings. It is only very rarely that any source is ascribed to the quote at all beyond Rutherford's name. Joel Beeke quoted the line, along with others, in The Quest for Full Assurance: The Legacy of Calvin and His Successors, p. 162, and provided a footnote to p. 52ff of the 1881 edition of his Letters; although the other quotes referenced on p. 162 are found there, this particular quote is not. However, there are some other lines in his Letters that seem to echo the thought, if not the exact language.
Letter 35 (First Part, June 15, 1637) [Letter 177 of Andrew Bonar's 1891 ed.] (p. 105 of Thomas Smith's 1881 ed.):
O, that my Master would take up house again, and lend me the keys of His wine-cellar again, and God send me borrowed drink till then.
Letter 50 (First Part, 1637) [Letter 249 of Andrew Bonar's 1891 ed.] (p. 129 of Thomas Smith's 1881 ed.):
But for you hing on, your feast is not far off; ye shall be filled ere ye go, there is as much in our Lord's pantry, as will satisfy all His bairns, and as much wine in His cellar as will quench all their thirst.
Letter 122 (First Part, June 15, 1637) [Letter 179 of Andrew Bonar's 1891 ed.] (p. 224 of Thomas Smith's 1881 ed.):
I wish, for my part, I could send you, and that gentleman who wrote his commendations to me, into the King's innermost cellar and house of wine to be filled with love. A drink of this love is worth the having indeed.
Letter 32 (Second Part, February 13, 1640) [Letter 295 of Andrew Bonar's 1891 ed.] (p. 431 of Thomas Smith's 1881 ed.):
Come, come, dear friend, and be pained, that the King's wine-cellar of free love, and His banqueting-house (O so wide, so stately! O so Godlike, so glory-like!) should be so abundant, so overflowing, and your shallow vessel so little, to take in some part of that love.
Letter 3 (Third Part, July 21, 1630) [Letter 12 of Andrew Bonar's 1891 ed.] (p. 488 of Thomas Smith's 1881 ed.):
You have been of late in the King's wine-cellar, where you were welcomed by the Lord of the inn, upon condition that ye would walk in love; put on love, and brotherly kindness, and long-suffering; wait as long upon the favour and turned hearts of your enemies, as your Christ waited upon you, and as dear Jesus stood at your soul's door with dewy and rainy locks, the long cold night; be angry but sin not.
I hope that if my research is incomplete and this quote is properly ascribed to Rutherford after all, that someone will kindly provide the citation. Regardless, may each child of God who finds himself or herself in the cellar of affliction drink deeply of the King's choice wine and be filled with his love.