The image below  is a screen shot  displaying Reliance of the Traveller, Book O, Ch.9.1 , as it appeared in my browser, which was pointed to  the search result from http://www.muhaddith.org/cgi-bin/e_optns.exe .  I had searched for each year because that phrase is used in the description of the obligation to attack Kuffar who are passively minding their own affairs at home.  This is a link to the ayat cited in the text: 4:95.

    See http://en.wikipedia.org/wiki/Fard for the details of the concept of obligation as communal and individual.  When Islam is the aggressor, the obligation is fard al-kifaya,  individuals are excused once a sufficient number have reported to the battle front. When kuffar  invade Muslim lands, the obligation is fard al-ayn, binding on all who are able to fight.

    Pay particular attention to the the text following the citation to 4:95. It informs us that there is an annually recurring obligation to attack kuffar.  Al Shafi'i has made the matter perfectly clear.
"The least that the imam must do is that he allow no year to pass without having organised a military expedition by himself, or by his raiding parties, according to the Muslims' interest, so that the jihad will only be stopped in a year for a (reasonable) excuse."
Reliance of the Traveller O9.1 Screenshot