The story of Tha’labah (the pigeon of the mosque) is not true

The story about the reason for revelation of the verse
(interpretation of the meaning): “And of them are some who made a
covenant with Allaah (saying): ‘If He bestowed on us of His Bounty…”
[al-Tawbah 9:74], which says that this refers to Tha’labah ibn Haatib,
does not have a sound isnaad. Tha’labah ibn Haatib was an Ansaari who is
counted among those who were present at Badr, and he was martyred on the day
of Uhud, as was affirmed by a number of scholars, including al-Haafiz Ibn
Hajar (may Allaah have mercy on him) 

And Allaah is the Source of strength. May Allaah send
blessings and peace upon our Prophet Muhammad and his family and companions.
End quote. 

Standing Committee for Academic Research and Issuing Fatwas 

Shaykh ‘Abd al-‘Azeez ibn ‘Abd-Allaah Aal al-Shaykh, Shaykh
‘Abd-Allaah ibn Ghadyaan, Shaykh Saalih al-Fawzaan, Shaykh Bakr Abu Zayd. 

Fataawa al-Lajnah al-Daa’imah li’l-Buhooth al-‘Ilmiyyah
wa’l-Ifta (26/49). 

Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said:
The words “And of them are some who made a covenant with Allaah…”
were revealed concerning some of the hypocrites. As for the widely-spread
idea that it was revealed concerning Tha’labah ibn Haatib in a lengthy story
that was narrated by many mufassireen and is spread by many preachers, this
report is da’eef (weak) and is not sound, and it is contrary to that which
no Muslim has any excuse for not knowing, which is that Allaah accepts the
repentance of anyone who repents from sin, no matter what the sin is. End
quote from Sharh Risaalah Usool fi’l-Tafseer.