"And inform them about the guests of Abraham, when they entered upon him and said, 'Peace.' He said, 'Indeed, we are apprehensive of you'" means: fearful.
Muhammad said: "Peace" (salaman) is in the accusative case as a verbal noun (masdar); as if he had said: "They greeted him with a greeting (salaman)."
﴿وَنَبِّئْهُمْ عَنْ ضَيْفِ إِبْرَاهِيمَ إِذْ دَخَلُوا عَلَيْهِ فَقَالُوا سَلامًا قَالَ إِنَّا مِنْكُم وجلون﴾ أَيْ: خَائِفُونَ.
قَالَ محمدٌ: (سَلامًا) منصوبٌ عَلَى الْمَصْدِرِ؛ كَأَنَّهُ قَالَ: فَسَلمُوا سَلاما.