I remember that there is some citation in Kohelet meaning "better peace and poor then rich and without peace", but cannot recall the exact source... Does someone remember?
Perhaps you refer to Koheles 5:11:
מְתוּקָה שְׁנַת הָעֹבֵד, אִם-מְעַט וְאִם-הַרְבֵּה יֹאכֵל; וְהַשָּׂבָע, לֶעָשִׁיר--אֵינֶנּוּ מַנִּיחַ לוֹ, לִישׁוֹן.
Sweet is the sleep of a labouring man, whether he eat little or much; but the satiety of the rich will not suffer him to sleep.
In fact, an evaluation of the condition of the rich and the poor is a recurring theme in Koheles.
I'm guessing you mean chapter 4 vs 6 better one handful peacefully than two handfuls of work and bad spirit.
I suspect that the answer already given (Kohelet 4:6) is the correct one; it might also be worth noting some proverbs that express the same sentiment:
15:16 Better a little with the fear of the Lord, than a great treasury and turmoil with it. 17 Better a repast of herbs where there is love, than a fattened ox where there is hatred.
17:1 Better a piece of dry bread and tranquility with it, than a house full of sacrifices of strife.