Ayesha reported,

She said to Urwa, "Nephew, your two fathers, Zubayr and Abu Bakr, were among them. When the Prophet of Allah suffered what he suffered on the day of Uhud and the polytheists withdrew from him, he feared they might return, so he asked, 'Who will go after them?' Seventy men volunteered from among them, and Abu Bakr and Zubayr were among them."

Azami 12103

Sahih

عن عائشة

قالت لعروة: يا ابن أختي كان أبواك منهم الزبير وأبو بكر، لما أصاب نبي الله ما أصاب يوم أحد، وانصرف عنه المشركون، خاف أن يرجعوا فقال: من يذهب في أثرهم؟ فانتدب منهم سبعون رجلا، قال: كان فيهم أبو بكر والزبير.

الأعظمي 12103صحيح
Contents
Reference
Commentary
Ayat
Collection
Jami al-Kamil
Book
Tafsir of the great Quran
Chapter
Virtues of Surah Baqarah
Section
His saying, "Those who responded to Allah and the Messenger after injury had struck them, for those who did good among them and feared Allah is a great reward"
Numbering
Jami al-Kamil 12103 (2nd edition)
Azami 12103