Mishnah for Bava Batra 7:2
לא יעמיד אדם תנור בתוך הבית אלא אם כן יש על גביו גובה ארבע אמות היה מעמידו בעלייה עד שיהא תחתיו מעזיבה שלשה טפחים ובכירה טפח ואם הזיק משלם מה שהזיק רבי שמעון אומר לא נאמרו כל השיעורין האילו אלא שאם הזיק יהא פטור מלשלם:
In standing up to recite the Prayer ('Amida), the feet must be met. There are two opinions on this subject, viz. that of R. Levi, and that of R. Shimon. The one says: it is to imitate the angels; the other says: it is to imitate the priests. The latter opinion is founded on the verse, " Neither shalt thou go up by steps to mine altar" (Exod. xx. 2); for the priests had to go to the altar by placing the toe beside the heel, and the heel beside the toe (i.e. by taking very little steps). The former opinion is based on the verse, " And their feet were straight feet" (Ezek. i. 7). Now, II. Hanina bar-Andira, in the name of R. Samuel bar-Zootai, says : The angels have no knee-joint, according to (Dan. vii. 16), " I came near unto one of them, that stood (always) by.'" R. Hoona says: If one sees the priests in the Synagogue at the time of their first blessing of the people, one must say: «' Bless the Lord, ye his angels" (Ps. ciii. 20); if at the second benediction: "Bless ye the Lord, all ye his hosts" (Ps. ciii. 21); if at the third benediction: "Bless the Lord, all his works" (Ps. ciii. 22). For the Prayer of Mousaph (additional)