Let a stranger praise you, not your mouth/ let another man praise you and not your own mouth/self-praise is no praise/ don't blow your own trumpet
Don't praise yourself; praise and compliments should come from others. A saying that calls for modesty and avoiding boasting.
("Let a stranger praise you, and not your mouth; a foreigner, and not your lips" - Proverbs 27:2, and likewise: "They said to Rav Pappa: What is your name? He said to them: Rav Pappa. They said to him: But is it not said: Let a stranger praise you and not your mouth? He said: And if there is no stranger - your mouth" - Sefer HaAggadah, rena, according to the Rashba's Responsa in the early responsa, peh-dalet, and likewise: "And he saw the clothes and said, 'Do you also know how to sew? A stranger praised you and not your mouth,' I answered" - S.Y. Agnon / In the Prime of Her Days)
Translation
Expression (Hebrew)
יְהַלֶּלְךָ זָר וְלֹא פִיךָ
Definition (Hebrew)
אַל תְּהַלֵּל אֶת עַצְמְךָ כִּי הַמַּחְמָאוֹת וְהַשְּׁבָחִים צְרִיכִים לְהַגִּיעַ מֵהַזּוּלָת.פִּתְגָּם הַקּוֹרֵא לִצְנִיעוּת שֶׁלֹּא לְהִתְרַבְרֵב.
("יְהַלֶּלְךָ זָר וְלֹא פִיךָ, נָכְרִי וְאַל שְׂפָתֶיךָ"- מִשְׁלֵי כז ב,וְכֵן:"אָמְרוּ לוֹ לְרַב פַּפָּא:מָה שִׁמְךָ?אָמַר לָהֶם:רַב פַּפָּא.אָמְרוּ לוֹ:וְהַלֹּא נֶאֱמַר:יְהַלֶּלְךָ זָר וְלֹא פִיךָ?-אָמַר:וְאִם אֵין זָר-פִּיךָ"-סֵפֶר הָאַגָּדָה רנא,ע"פ תְּשׁוּבוֹת הָרַשְׁבָּ"א בָּרִאשׁוֹנוֹת פֵּד,וְכֵן:"וַיַּרְא אֶת הַבְּגָדִים וַיֹּאמֶר , גַּם מְלֶאכֶת הַתְּפִירָה יָדַעְתָּ ? יְהַלֶּלְךָ זָר וְלֹא פִיךָ עָנִיתִי"- שַׁ"י עַגְנוֹן / בִּדְמֵי יָמֶיהָ)