Did Ali ibn al-Husayn hear from Ali ibn Abi Talib (may Allah be pleased with them both)?

Ali ibn al-Husayn ibn Ali ibn Abi Talib (Zayn al-Abidin) did not hear from his grandfather Ali ibn Abi Talib. Therefore, what he narrates from him without an intermediary is considered to have a broken chain of transmission (disconnected sanad). However, this discontinuity does not weaken all narrations; such narrations may be strengthened by other chains or corroborating evidence, as is the case with the hadith: "Whoever is killed defending his property is a martyr."

The chain of transmission in Musnad Ahmad: "from his father, from his grandfather"; it is possible that the grandfather is al-Husayn ibn Ali, in which case the chain would be continuous and sound. If the grandfather is Ali ibn Abi Talib, then the chain would be disconnected. Nevertheless, the hadith is authentic and has strong corroborating evidence, including what was narrated by al-Bukhari and Muslim from Abdullah ibn Amr.