The saying of Allah, exalted be His praise: "When you contract a debt with one another for a fixed term, write it down." [Surah al-Baqarah: 282]
And in its context He said: "And call two witnesses from among your men; and if there are not two men, then one man and two women from among those whom you accept as witnesses, so that if one of the two (women) forgets, the other can remind her." [Surah al-Baqarah: 282]
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / Q20529