If the lines are from Nicholson's complete translation of alll six books, then all that is needed is one or more lines, or even a few consecutive words. Feel free to send an e-mail to this website and type "Masnavi search" in the subject area. Then the full quote requested, plus the Masnavi book and verse numbers can then be given.
Or you can search the Masnavi yourself via the "Nich. trans." links at the beginning of the Links page on this website, using word(s) searches using three links: Books I&II, Books III&IV, and Books V&VI.
If the lines are from one of Coleman Barks' versions (based on Nicholson's translation), it may be more difficult to locate the corresponding verses in Nicholson's translation, but this may be possible via a single-word search.
Verses can be found as long as they exist in Nicholson's Persian text (consisting of 25,632 verses). Any verse not found in his edition can be assumed to be from an "expanded editions" of the Masnavi containing over two thousand verses added to the Masnavi over the centuries, and therefore not in the earliest manuscripts. (Although it is possible that it is a verse existing in the earliest manuscript of the Masnavi, which was not available to Nicholson until he had already published his edition Books I, II, and had translated 3/5 of Book III.)
Searches are not limited to just the last few words of a verse, but can involve a few consecutive words anywhere in the Masnavi. Send an e-mail to this website and type "Masnavi search" in the subject area. The Masnavi book and "Nicholson verse number" can then be given, as well as the corresponding Nicholson translation (if desired).