Musical compositions can be, and if recent almost always are, protected by copyright. This is separate from the copyright on a recording of a performance of the work.
If you reuse a musical passage, the new work may be a derivative work, that is a work based on an earlier work. Or an extended musical quotation could be considered to be copyright infringement.
If this is in the united-states the use of a section from a previous work might be considered to be a fair use (fair-use). This is a specifically US concept in copyright law, although several other countries have a concept of fair dealing which is somewhat similar, although narrower.
Whether a use is a fair use is an inherently fact-based determination. There is no clear and simple bright line for what is and is not a fair use. US law (17 USC 197) specifies four factors which are to be weighed by a court in considering the matter:
The purpose and character of the use. If your use is commercial that weighs against fair use, but does not at all preclude it. This factor also includes whether the use is transformative or not. A transformative use is one that takes the part used for a very different sort of purpose than the original. Parodies are normally transformative, for example. A quote for purposes of commentary and analysis, or criticism is normally transformative. Transformative uses are more likely to be considered fair uses.
The nature of the copyrighted work. Creative works such as fiction and music are more strongly protected than works such as textbooks and news stories. This probably weighs against fair use in the case described.
The amount and substantiality of the portion used in relation to the copyrighted work as a whole. If only a short section of a longer work is used, that weighs in favor of fair use. However very short quotes can still fail, to be held to be fair uses. In Harper vs Nation a quote of about 300 words from a 500 page book was held not to be fair use because it was "the heart of the book".
The effect of the use upon the potential market for or value of the copyrighted work. A use that significantly harms the market value of the original, or serves as a replacement for it, weigh strongly against fair use. This was a major factor in Harper vs Nation.
Each case of claimed fair use is evaluated by looking at all four factors, and the specific facts of the case.
From the description in the question, such a use might well be held to be fair use. Musical quotations often are. But there is no way to be sure unless a court evaluates the specific case. A lawyer specifically experienced in not only copyright law, but copyrights on music, might be able to give more specific advice.
Or you could, of course, seek permission from the copyright holder, quite likely the original composer or artist. If you get permission, there is no further issue. There might be a charge, but when the use is minor, and has no commercial effect, the charge might be small or even zero provided that the source is acknowledged.
