Is declaring a debt forgiveness as a 'charity' (Sadaqah) valid?

Primary text

It is valid if the creditor states, 'I gave it to you as charity' (Tasadadtu bihi 'alayka). This ruling is supported by the Quranic text concerning the blood money (Diyah) for a believing slave whose killer forgives it: {unless they give it as charity} (Quran 4:92).