Tha`labah and the account about Zakah

Q 2: It is mentioned in: "Tafsir Al-Tabary" on the authority of Ibn ‘Abbas (may Allah be pleased with them both) that an Ayah (Qur’anic verse) was revealed about Tha‘labah. However, some of our brothers told me that he was not there at that time, thereby refuting Al-Hafiz Ibn Hajar. Is the story about Tha‘labah not true then? He was called, "Hamamat Al-Masjid (the Pigeon of the Mosque)" and he was one of the Ansar (Helpers, inhabitants of Madinah who supported the Prophet). What is the truth of this matter? (Part No. 26; Page No. 50

A: The account given about the reason for the Revelation of the Saying of Allah (Exalted be He): And of them are some who made a covenant with Allâh (saying): "If He bestowed on us of His Bounty which is said to refer to Tha‘labah ibn Hatib, does not have a sound Isnad (chain of narrators). Tha‘labah ibn Hatib was an Ansary, and one among the few who participated in the Battle of Badr and was martyred on the day of the Battle of Uhud. This has been confirmed by a number of scholars; including Al-Hafiz Ibn Hajar (may Allah be merciful to him).May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.