In the meditation after each Shmoneh Esrei, we read the line which includes the words בתורתך, מצותיך תרדוף. This comes from the prayer of Mar Brei D'ravina on Brachot 17a. But in my siddur Tefillah Hashalem (page 282), in the Shabbat Mincha davening, the word ואחרי is added before מצותיך .
It isn't added in any other davening that I have found in my siddur nor did I see it in the Koren or Artscrolls I had handy, but a quick look online reveals that this version appears in a variety of siddurim. What I didn't see was any explanation as to why in those other sources, the word is added. Is there another gemara text which has the meditation with it included? Is there a pasuk this is based on, or some other source for the prayer which is worded with acharei?