Abdullah bin Abbas (may Allah be pleased with them both) was asked about this verse: 'nor should they leave, unless they commit a clear immorality' [Surah al-Talaq: 1], and he said: 'A clear immorality' means that the woman uses foul language against the man's family and harms them.
Imam al-Shafi'i (may Allah have mercy on him) said: The Sunnah of the Messenger of Allah (peace and blessings be upon him) in the hadith of Fatimah bint Qays (may Allah be pleased with her) indicates that what Abdullah bin Abbas (may Allah be pleased with them both) interpreted regarding the saying of Allah Almighty, 'unless they commit a clear immorality' [Surah al-Nisa: 19], is foul language against her husband's family, as he interpreted it, if Allah Almighty wills.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العدد / 15485