Dear Abdalrahman,

In case of MATLAB in general, I have seen (and have used myself) the following form for citing MATLAB: "MATLAB 2014a, The MathWorks, Natick, 2014." (or whatever version you are using). If you are using a specific toolbox available online, it might be a good idea and helpful to the reader to give, e.g., the name and URL of the specific toolbox. 

Dear Abdalrahman,

If the toolbox you want to cite is described in a publication you could cite it, for example:

"The spectral centroid (weighted mean of spectrum energy) reflects the global spectral distribution and has been used to describe the timber, whereas the spectral flux conveys spectrotemporal information (variation of the spectrum over time) (Marozeau et al., 2003; MIRtoolbox; Lartillot et al., 2008).

Lartillot, O., Toiviainen, P., Eerola, T. (2008). A matlab toolbox for music information retrieval. In: Preisach, C., Burkhardt, H., Schmidt-Thieme, L., Decker, R., editors. Data Analysis, Machine Learning and Applications: Studies in Classification, Data Analysis,  and Knowledge Organization. Berlin, Germany: Springer, pp. 261–8."

Otherwise, as Pekko advises, you should specify the url from where the toolbox could be downloaded. Remember to add the access date when you are referencing the url.

Cheers! 

To cite MATLAB (and in this case a toolbox) you can use this:

MATLAB and Statistics Toolbox Release 2012b, The MathWorks, Inc., Natick, Massachusetts, United States.

Actually, this is the main challenges for all software developers and programmers or those who use computer software.  This very much depends upon the style guidelines recommended for your paper. If there is a recommended citation then use it. If there is no recommended citation from the software publishers, then I'd suggest that your citations contain the following information:

1.      MATLAB and Statistics Toolbox Release 2012b, The MathWorks, Inc., Natick, Massachusetts, United States.

2.       MATLAB 8.0 and Statistics Toolbox 8.1, The MathWorks, Inc., Natick, Massachusetts, United States.

You can cite it as follows:

"The Psychophysics Toolbox (Brainard 1997, Pelli, 1997) is a software package that adds the ability for precise stimulus specification to MATLAB, a high-level interpreted language with extensive support for numerical calculations (The MathWorks, 1993), allowing for rapid and flexible programming of psychophysical experiments.

The MathWorks. (1993). MATLAB User's Guide. The MathWorks, Inc., Natick, MA."

Latest MATLAB 2018a referencing style:

MATLAB 2018a, The MathWorks, Inc., Natick, Massachusetts, United States.