Is a small amount of impurity and a minor obstruction in ablution forgiven, even if it were possible to remove them but we did not do so?

An impediment to Wudu (ablution), such as dirt under the fingernail, is overlooked due to hardship, but it is recommended to remove it to avoid divergence of opinion. Avoiding impurity is conditional upon knowledge and ability. And whoever is unable to remove what prevents water from reaching [the skin] may wipe over it.