Is it prohibited if we went to trade in our gold jewellery and upgrade it for more expensive gold by adding cash?
Alhamdulillah, praise and gratitude to Allah SWT for His countless blessings for us all. Praise and salutations to our beloved Prophet Muhammad PBUH, his family, companions, and all those who follow his footsteps until the Final day.
Gold is a ribawi item of which it is obligatory for us to be cautious in its trade as stated in a hadith narrated from ‘Ubadah bin al-Somit RA, where the Prophet Muhammad PBUH said:
الذَّهَبُ بالذَّهَبِ، والْفِضَّةُ بالفِضَّةِ، والْبُرُّ بالبُرِّ، والشَّعِيرُ بالشَّعِيرِ، والتَّمْرُ بالتَّمْرِ، والْمِلْحُ بالمِلْحِ، مِثْلًا بمِثْلٍ، سَواءً بسَواءٍ، يَدًا بيَدٍ، فإذا اخْتَلَفَتْ هذِه الأصْنافُ، فَبِيعُوا كيفَ شِئْتُمْ، إذا كانَ يَدًا بيَدٍ
“Gold is to be paid for with gold, silver with silver, wheat with wheat, barley with barley, dates with dates, and salt with salt, same quantity for same quantity and equal for equal, hand to hand (i.e. payment being made on the spot). If these classes differ, sell as you wish as long as payment is made on the spot.” 
There are two important matters in the trade of ribawi items to ensure that the transaction is permissible, which are:
- “YAdan bin yadin.” This refers to the sanctioning of taqabudh, which is the handover of two items. The handover is valid through hissi, which means physical and direct between two parties, or hukmi, such as through a proxy.
- “Mithlin bi mithlin.” This refers to a comparable and similar.
According to the above question, the ruling of gold trade-in with the addition of some money is permissible according to syarak. We suggest, first selling the gold, then buying the one with a higher value. This is the correct way taught by Rasullullah PBUH as stated in a hadith narrated from Abu Sa’id al-Khudri, he said:
جَاءَ بِلاَلٌ إِلَى النَّبِيِّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ بِتَمْرٍ بَرْنِيٍّ، فَقَالَ لَهُ النَّبِيُّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ: مِنْ أَيْنَ هَذَا؟، قَالَ بِلاَلٌ: كَانَ عِنْدَنَا تَمْرٌ رَدِيٌّ، فَبِعْتُ مِنْهُ صَاعَيْنِ بِصَاعٍ، لِنُطْعِمَ النَّبِيَّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ، فَقَالَ النَّبِيُّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ عِنْدَ ذَلِكَ: أَوَّهْ أَوَّهْ، عَيْنُ الرِّبَا عَيْنُ الرِّبَا، لاَ تَفْعَلْ، وَلَكِنْ إِذَا أَرَدْتَ أَنْ تَشْتَرِيَ فَبِعِ التَّمْرَ بِبَيْعٍ آخَرَ، ثُمَّ اشْتَرِهِ
Bilal brought the Prophet some barni* dates, and when he asked him where he had got them he replied, “I had some inferior dates, so I sold two sa’s of them for a sa.” He said, “Ah, the very essence of usury, the very essence of usury. Do not do so, but when you wish to buy, sell the dates in a separate transaction, then buy with what you get.” 
A clear solution can be found in this hadith in order to avoid usury in trade and that is to sell the cheaper gold then buy the more expensive gold at its appropriate price. Let us all learn our religion better so that we’ll be able to avoid ourselves from getting involved in matters that are prohibited in Islam.
May Allah SWT ease our affairs and grant us understanding in this religion. Amin.