Mujahid bin Jabir مجاهد بن جبر · The Book on Fasting

"A woman came to the Prophet and said: 'My sister died while she had two consecutive months of fasting due.' So he said: 'Do you not see that if there was a debt due from your sister then you would have to pay it?' She said: 'Yes.' He said: 'Then the right of Allah is more appropriate.'"