Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: "The people were leaving in every direction (without performing the farewell tawaf), so the Messenger of Allah (peace and blessings be upon him) said: 'Let no one depart (from Makkah) until his last act is (the tawaf of) the House of Allah.'"
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10940