sources mekorot - Can we hasten Moshiach's coming through the mitzvah of ואהבת לרעך כמוך?

In Jewish singer Meilech Kohn's song, "Veuhavtu", he expresses an interesting thought in the lyrics:

.יעדער איינער דאווענט און בעט און מ'ווארט פאר משיח, ער וועט נאר קומען ווען מיר פארטראגן זיך

"Everyone prays and begs and waits for Moshiach; he will only come when we all get along."

This is a nice idea, however, I've never heard it expressed in any sources. Is there a source for this idea, that through the mitzvah of ואהבת לרעך כמוך we can merit Moshiach?

^{By the way, an a capella version of the song can be found here from Ari Goldwag.}

Answer

This idea can be found in Medrash Tanchuma, Nitzavim 1:

וְכֵן אַתְּ מוֹצֵא שֶׁאֵין יִשְׂרָאֵל נִגְאֲלִין עַד שֶׁיִּהְיוּ כֻּלָּן אֲגֻדָּה אַחַת, שֶׁנֶּאֱמַר: בַּיָּמִים הָהֵמָּה וּבָעֵת הַהִיא נְאֻם ה' יָבֹאוּ בְנֵי יִשְׂרָאֵל וּבְנֵי יְהוּדָה יַחְדָּו וְגוֹ' (ירמיה נ, ד). כְּשֶׁהֵן אֲגוּדִים, מְקַבְּלִין פְּנֵי שְׁכִינָה

Yisroel will not be redeemed until they will all be one group, as it says: "In those days and at that time—declares the LORD—the people of Israel together with the people of Judah shall come, etc." (Yirmiya 50:4) When they are a group, they receive the face of the shchina