וַיָּ֣עָף אֵלַ֗י אֶחָד֙ מִן־הַשְּׂרָפִ֔ים וּבְיָד֖וֹ רִצְפָּ֑ה בְּמֶ֨לְקַחַ֔יִם לָקַ֖ח מֵעַ֥ל הַמִּזְבֵּֽחַ׃
Then flew unto me one of the seraphim, with a glowing stone in his hand, which he had taken with the tongs from off the altar;
Rashi on Isaiah
a glowing coal Heb. רִצְפָּה, a coal, and similarly, (I Kings 19:6) “a cake baked on hot coals (עֻגַּתרְצָפִים),” like עֻגַּתרְשָׁפִים. In regards to Isaiah and Elijah, however, it is written with a ‘zadi,’ רִצְפָּה, because they spoke ill of Israel. This one [Isaiah] called them a people of unclean lips, and this one [Elijah] said, (ibid. 10) “For...have forsaken Your covenant.” Said the Holy One, blessed be He, to the angel, “Break the mouth (רְצוֹץפֶּה) that spoke ill of My children.”
Ibn Ezra on Isaiah
ויעׇף Then flew. As written here, with a short kamez under ע, it is derived from עוף to fly; but ויעַף (Jud. 4:21), where the ע has a pathah, is derived from עיף to be weary.