ציטירנדיקער פּירוש אויף תהילים 126:1

The destruction of the Temple - The Shl"a wrote that at every meal, one should recite "Al naharot Bavel" ("By the Rivers of Babylon..." - Psalms 137:1). And on Shabbat, and also on days that Tachanun is not said, one should say "Shir Hama'alot b'shuv Hashem..." ("A song of ascents. When the Lord returns..." - Psalms 126:1). And the main thing is to know/understand what one is saying, and to have concentration.

You carry them away as a flood; they are like a sleep Now you have seized those years and had them become a few days, which are merely like a sleep of slumber, for the years of the generations are seventy years, as is explained at the end of the chapter: “The days of our years because of them are seventy years,” and they are regarded as one sleep. As the matter that is said (below 126:1) “When the Lord returns the returnees to Zion, we shall be like dreamers.” This was stated regarding the Babylonian exile, which lasted seventy years.