It is narrated from Sayyiduna Ali (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "The Hour will not be established (until all of my companions have completely departed from this world); to the extent that one of my companions will be sought as something lost is sought, but not a single companion will be found."
Hadith Referenceمسند احمد / مسند الخلفاء الراشدين / 675
Hadith Gradingحکم دارالسلام:إسناده ضعيف لضعف الحارث الأعور