S1·E22 Eye of the Beholder

While Darrin, Samantha and Endora are browsing through an antiques store, Endora believes it's time Darrin suspected that Samantha may not be as young as her mortal equivalent would be. Darrin sees a 300-year-old painting, "Maid of Salem", which bears a striking resemblance to Samantha, causing him to question her age and their relationship. As Darrin contemplates his future with Samantha under these circumstances, Samantha has to figure out a way to save her marriage if the truth truly does comes to light.