When Ash returns to Pallet Town in the first series, I think after he got all the badges and was preparing for the Pokemon League Championships. When they were in Professor Oak's lab, Oak showed off Ash's extra pokemon that was sent to him pointing out that most were Tauros caught in the Safari Zone.
When I first saw the series I didn't recall it ever showing that Ash went there. So I am wondering if Ash's time in Kanto's Safari Zone was ever detailed anywhere, like why he caught nothing but Tauros or what happened in regards to Pikachu (as in the games you aren't allowed to take pokemon into the Safari Zone and I think it was the same in Yellow where you no longer have Pikachu follow you in there until you leave).