Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said about a man who was owed 20 dirhams by another man: he kept giving him gifts, and whenever he gave him a gift he sold it, until its price reached 13 dirhams. So Ibn Abbas (may Allah be pleased with them both) said: Take seven dirhams from him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10930