What is the right way to exchange your old gold necklace that has 40 grams of 22K gold for new gold necklace that has 60 grams of 22k gold?

At the Jewelry shop:

Have the jeweler weigh your old necklace and sell it to him at a certain cash price. Receive the cash from the Jeweler, then in another transaction buy the new necklace from him and pay him the new price in cash.

Make sure not to just exchange the old one with the new one even if the Jeweler told you to do so. This kind of exchange is not allowed and it's called Ribal-Fadl (surplus Riba). The reason is that each gold necklace contain a different quantity of gold and gold has to be exchanged like for like - similar quantity to similar quantity as mentioned in the Hadith of Prophet MuHammad, Sallal-Laahu ^Alayhi Wa Sallam related by Imam Bukhary and Imam Muslim.

The Prophet صلى الله عليه وسلم said what means:

“Donot sell gold for gold unless it is thesame amount for the same amount,and do not make one amount greater than the other."

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