"heart. Maddened with rage, he declared that the whole family of the priest should perish. And the terrible decree was executed. Not only Ahimelech, but the members of his father's house—“four-score and five persons that did wear a linen ephod”—were slain at the king's command, by the murderous hand of Doeg. PP 659.1"
"And the king said to Doeg, Turn thou, and fall upon the priests. And Doeg the Edomite turned, and he fell upon the priests, and slew on that day fourscore and five persons that did wear a linen ephod."
The EGW passage directly references the slaughter of the priests by Doeg, including the number of victims and their attire (linen ephod), as described in 1 Samuel 22:18.
"“And Nob, the city of the priests, smote he with the edge of the sword, both men and women, children and sucklings, and oxen, and asses, and sheep.” This is what Saul could do under the control of Satan. When God had said that the iniquity of the Amalekites was full, and had commanded him to destroy them utterly, he thought himself too compassionate to execute the divine sentence, and he spared that which was devoted to destruction; but now, without a command from God, under the guidance of Satan, he could slay the priests of the Lord and bring ruin upon the inhabitants of Nob. Such is the perversity of the human heart that has refused the guidance of God. PP 659.2"
"Now go and smite Amalek, and utterly destroy all that they have, and spare them not; but slay both man and woman, infant and suckling, ox and sheep, camel and ass."
The EGW passage directly contrasts Saul's disobedience in sparing the Amalekites with his later, even more egregious, act of slaughtering the priests at Nob. The verse from 1 Samuel 15:3 is the basis for the first part of the contrast, highlighting Saul's initial disobedience.