Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
darimi:609Muḥammad b. Kathīr > al-Awzāʿī > Makḥūl

[Machine] In English, the translation of the given sentence is: "There are two types of Sunnah; a Sunnah that is obligatory to follow and leaving it is considered a sin, and a Sunnah that is recommended to follow but leaving it is not a matter of concern."  

الدارمي:٦٠٩أَخْبَرَنَا مُحَمَّدُ بْنُ كَثِيرٍ عَنِ الْأَوْزَاعِيِّ عَنْ مَكْحُولٍ قَالَ

السُّنَّةُ سُنَّتَانِ سُنَّةٌ الْأَخْذُ بِهَا فَرِيضَةٌ وَتَرْكُهَا كُفْرٌ وَسُنَّةٌ الْأَخْذُ بِهَا فَضِيلَةٌ وَتَرْكُهَا إِلَى غَيْرِ حَرَجٍ