مَطْلُ الْغَنِيِّ ظُلْمٌ
Delaying repayment by someone able to pay is an injustice.
Source: Bukhari and Muslim (al-Shaykhan).
مَطْلُ means evasive delay; الْغَنِيِّ refers here to a debtor with the means to pay; and ظُلْمٌ means injustice. The warning concerns someone who withholds a due payment despite being able to meet it.
مَطْلُ الْغَنِيِّ is an iḍāfah construction: مَطْلُ is the first noun and الْغَنِيِّ the genitive second noun. The whole expression is the subject of the sentence, while ظُلْمٌ is its predicate. This identifies the particular delay being condemned.
Taking repayment seriously is part of integrity. The bare fact that a payment was late does not establish the debtor's financial capacity.