جامع الترمذي

Narrated Ibn 'Abbas: from 'Umar bin Al-Khattab, who said: "The Prophet (ﷺ) looked over the idolaters, and there were a thousand of them, while his Companions were three-hundred and ten and some odd number of men. So the Prophet (ﷺ) of Allah (ﷺ) faced the Qiblah, stretched forth his hands and began beseeching his Lord: 'O Allah! Fulfill what You promised for me. [O Allah! Bring about what You promised for me] O Allah! If you destroy this band of adherents to Islam, you will not be worshiped upon the earth,' He continued beseeching his Lord with his hands stretched, facing the Qiblah until his Rida fell from his shoulders. Abu Bakr came to him, took his Rida and placed it back upon his shoulders, then embraced him from behind and said: 'O Prophet of Allah! You have sufficiently beseeched your Lord, indeed He shall fulfill what He promised you.' So Allah, Blessed and Most High, revealed: When you sought help of your Lord and He answered you (saying): 'I will help you with a thousand of the angels in succession (8:9).'

[Abu 'Eisa said:] This Hadith is Hasan Sahih Gharib. We do not know of it as a Hadith of 'Umar, except through the narration of 'Ikrimah bin 'Ammar, from Abu Zumail, and Abu Zumail's name is Simãk Al-Hanafi. And this was on the Day of Badr.