BH
Does it say in Rambam that a person in the presence of his teacher should always look at his face and never show him his back? If yes what is the Halacha’s source?
There are two Gemaras that come to mind both based off a pasuk in Yeshaya...
A Gemara in Eruvin 13b:
אָמַר רַבִּי: הַאי דִּמְחַדַּדְנָא מֵחַבְרַאי דַּחֲזִיתֵיהּ לְרַבִּי מֵאִיר מֵאֲחוֹרֵיהּ, וְאִילּוּ חֲזִיתֵיהּ מִקַּמֵּיהּ הֲוָה מְחַדַּדְנָא טְפֵי — דִּכְתִיב: ״וְהָיוּ עֵינֶיךָ רוֹאוֹת אֶת מוֹרֶיךָ״
The Gemara relates that Rabbi Yehuda HaNasi said: The fact that I am more incisive than my colleagues is due to the fact that I saw Rabbi Meir from behind, i.e., I sat behind him when I was his student. Had I seen him from the front, I would be even more incisive, as it is written: “And your eyes shall see your teacher” (Isaiah 30:20). Seeing the face of one’s teacher increases one’s understanding and sharpens one’s mind. (William Davidson translation & notation)
Also note Kerisus 6a:
אֲמַר לְהוּ רַב מְשַׁרְשְׁיָא לִבְנֵיהּ: כִּי בָּעֵיתוּ לְמֵיזֵל לְמִגְמַר קַמֵּי רַבְּכוֹן, גְּרוּסוּ מֵעִיקָּרָא מַתְנִיתִין וַהֲדַר עוּלוּ קַמֵּי רַבְּכוֹן, וְכִי יָתְבִיתוּ קַמֵּי רַבְּכוֹן, חֲזוֹ לְפוּמֵּיהּ דְּרַבְּכוֹן, שֶׁנֶּאֱמַר: ״וְהָיוּ עֵינֶיךָ רוֹאוֹת אֶת מוֹרֶיךָ״, וְכִי גָּרְסִיתוּ שְׁמַעְתָּא, גְּרוּסוּ עַל מַיָּא, דְּכִי הֵיכִי דְּמָשְׁכִי מַיָּא תִּמְשׁוֹךְ שְׁמַעְתְּכוֹן
With regard to positive omens, Rav Mesharshiyya said to his sons: When you want to go to study in the presence of your teacher, initially study the mishnayot and then ascend before your teacher. And when you sit before your teacher, see your teacher’s mouth, as it is stated: “And your eyes shall see your teacher” (Isaiah 30:20). And when you learn a halakha, learn near a source of flowing water, as just as the water flow continues, so too, your learning should continue. (Davidson translation & notation)
Rambam in Mishneh Torah, Talmud Torah 4:2 writes:
כֵּיצַד מְלַמְּדִים. הָרַב יוֹשֵׁב בָּרֹאשׁ וְהַתַּלְמִידִים מֻקָּפִים לְפָנָיו כַּעֲטָרָה כְּדֵי שֶׁיְּהוּ כֻּלָּם רוֹאִים הָרַב וְשׁוֹמְעִים דְּבָרָיו. וְלֹא יֵשֵׁב הָרַב עַל הַכִּסֵּא וְתַלְמִידָיו עַל הַקַּרְקַע אֶלָּא אוֹ הַכּל עַל הָאָרֶץ אוֹ הַכּל עַל הַכִּסְאוֹת. וּבָרִאשׁוֹנָה הָיָה הָרַב יוֹשֵׁב וְהַתַּלְמִידִים עוֹמְדִים וּמִקֹּדֶם חֻרְבַּן בַּיִת שֵׁנִי נָהֲגוּ הַכּל לְלַמֵּד לַתַּלְמִידִים וְהֵם יוֹשְׁבִים
How is [Torah] taught? The teacher sits at the head and the students sit around him, so that all can see the teacher and hear his words. The teacher should not sit on a chair, [while] his students [sit] on the ground. Rather, either everyone should sit on the ground or everyone should sit on chairs. Originally, the teacher would sit and the students would stand. [However,] before the destruction of the Second Temple, everyone followed the practice of teaching while both they and the students were seated.