question #1 Sahih al-Bukhari 2060, 2061, Book 34, Hadith 14 : What are the conditions for the permissibility of money exchange in Islamic trade?

I used to practice money exchange, and I asked Zaid bin ‘Arqam about it, and he narrated what the
Prophet said in the following: Abu Al-Minhal said, “I asked Al-Bara’ bin `Azib and Zaid bin Arqam
about practicing money exchange. They replied, ‘We were traders in the time of Allah’s Messenger (ﷺ) and I
asked Allah’s Messenger (ﷺ) about money exchange. He replied, ‘If it is from hand to hand, there is no harm
in it; otherwise it is not permissible.”