Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrates that the Prophet (peace and blessings be upon him) said: "Patience is at the first shock."
Imam al-Bazzar recorded it. Its chain contains a narrator, al-Waqidi, about whom there has been much criticism, though he has also been declared trustworthy.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الجنائز / 3955