Some writers claim that Aristotle has 4 predicables: definition, preperty, genus & accident; some other writers however claim 5 with the additional differentia. So what exactly is the case strictly according to Aristotle? Thank you.
Accoding to Topics, they are four; see 101b11-101b29:
arguments start with propositions, while the subjects on which deductions take place are problems. Now every proposition and every problem indicates either a genus or a property or an accident — for the differentia too, being generic, should be ranked together with the genus. Since, however, of what is proper to anything part signifies its essence, while part does not, let us divide the proper into both the aforesaid parts, and call that part which indicates the essence a definition, while of the remainder let us adopt the terminology which is generally current about these things, and speak of it as a property.
What we have said, then, makes it clear that according to our present division, the elements turn out to be four, all told, namely either property or definition or genus or accident.
there are four kinds in which [...]: definition, distictive property, genus and accidental [...]
It seems that with Porphyry (c.234 – c.305 AD)'s Eisagōgḗ, one of the most familiar handbooks of logic in the early Middle Ages, the predicables (commonly known under the title quinque voces) became five, with "species" in place of "definition".
Thus, as is apparent from the above text, Topics itself strongly supports the traditional fivefold classification.
See also 103b20:
Next, then, we must distinguish between the categories of predication in which the four above-mentioned are found. These are ten in number: What a thing is, Quantity, Quality, Relation, Place, Time, Position, State, Activity, Passivity. [See Aristolte's Logic: Categories and Aristotle's Categories].
Thus, in the analysis of the basic relation of "predication" (katêgorein) we have a (quite obscure) interplay between "types of predication" and "categories" (katêgoria).
See e.g. Michael Frede, Categories in Aristotle.