A collector knocked on my door asking for charity, after showing me the required documentation.. As I was ready to give him a donation which I had in my left hand, he wouldn’t accept it and said that one should give tzedaka money with the right hand only-even if you are left handed. He told me that he learned this at his kolel. I switched hands and he took the money! The reason for this, he said, was spiritual, but he couldn’t give me an answer regarding where this idea comes from.Is there a source in Yiddishkeit for this?

Shalom, How wonderful it is that even the charity collectors spread Torah! (I hope that his teaching was expressed in a polite and gentle fashion, and that no offence was taken). In general there is a preference of the right over the left. This is expressed in the verse in Tehillim (118,15) "Yemin Hashem Osah Chayil" , "G-d's right hand does valiantly". So we generally give preference to the right side, washing our right hand first, and putting our right shoe on first. So too when we hold an object of a mitzvah in our hands, such as the cup of wine for kiddush, we hold it in our right hand, to show its importance. When holding food in our hand before saying a blessing on it we also hold it in the right hand. Based on this it makes sense that the money to be given to charity, which is a mitzvah, should be held in the right hand to show that it is important and not being given "backhandedly". All this is found in Jewish law, halacha, and based, as I wrote, on the idea that the right hand side is more important. This being so, someone who is left handed would use their left hand instead of the right to show importance, as for them the left hand is indeed the stronger, more important hand. This is how the Ashkenazim rule. However the Sephardi Jews follow the kabbalistic teachings that say that even a left-handed person should hold the mitzvah in their right hand - as the right-hand side is spiritually always on the right. (See, for example, the laws of shaking Lulav and etrog, where the Ashkenazi and Sephardi traditions are explained (Shulchan Aruch, OH 651,3)). Beyond this, there is a kabbalistic teaching in the name of the Ari Hakadosh (Or Zadikim 2,63) which states that all charity should be given with the right hand, and even a left-handed person should do so. This is based on a midrash (Devarim Raba (parsha 5) which says that "two things are in the right hand of the Holy One - charity and Torah. Charity, as it says (Tehillim 48) Charity fills your right hand"...". The Maharal explains this concept in his Netivot Olam (Netiv Torah 16) that the right hand is able to spread out easily to give, whereas the left hand is weaker, and is therefore the side of receiving. There are, of course, many deeper and more mystical kabbalistic explanations of the meaning of "right" and "left". The Ben Ish Hai (Parshat Vayigash, 13) also mentions using the right hand. He adds that the coin represents the letter yod, the right hand the letter hey (because the five fingers are equal to the numeric value of the letter hey, 5), the arm the letter vav, which is stretched out like a vav, and the left hand of the receiver another letter hey - together the letters of Hashem's name. Blessings.