It was narrated that Jabir bin 'Abdullah said:

"We were traveling with the Messenger of Allah and I was riding a camel. The Messenger of Allah said to me: 'Will you sell it to me for such and such, may Allah forgive you?', I said, I said, 'Yes, it is yours, O Prophet (ﷺ) of Allah.' He said: 'Will you sell it to me for such and such, may Allah forgive your?' I said: 'Yes, it is yours, O Prophet (ﷺ) of "Allah.' He said: 'Will you sell it to me for such and such, may Allah forgives you?' I said: 'Yes, it is yours. '''(One of the narrators) Abu Nadrah said: "This became a phrase that was used by the Muslims: 'Do such and such, may Allah forgive you.

أَخْبَرَنَا مُحَمَّدُ بْنُ عَبْدِ الأَعْلَى، قَالَ حَدَّثَنَا الْمُعْتَمِرُ، قَالَ سَمِعْتُ أَبِي قَالَ، حَدَّثَنَا أَبُو نَضْرَةَ، عَنْ جَابِرِ بْنِ عَبْدِ اللَّهِ، قَالَ كُنَّا نَسِيرُ مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم وَأَنَا عَلَى نَاضِحٍ فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ أَتَبِيعُنِيهِ بِكَذَا وَكَذَا وَاللَّهُ يَغْفِرُ لَكَ ‏"‏ ‏.‏ قُلْتُ نَعَمْ هُوَ لَكَ يَا نَبِيَّ اللَّهِ قَالَ ‏"‏ أَتَبِيعُنِيهِ بِكَذَا وَكَذَا وَاللَّهُ يَغْفِرُ لَكَ ‏"‏ ‏.‏ قُلْتُ نَعَمْ هُوَ لَكَ يَا نَبِيَّ اللَّهِ ‏.‏ قَالَ ‏"‏ أَتَبِيعُنِيهِ بِكَذَا وَكَذَا وَاللَّهُ يَغْفِرُ لَكَ ‏"‏ ‏.‏ قُلْتُ نَعَمْ هُوَ لَكَ ‏.‏ قَالَ أَبُو نَضْرَةَ وَكَانَتْ كَلِمَةً يَقُولُهَا الْمُسْلِمُونَ افْعَلْ كَذَا وَكَذَا وَاللَّهُ يَغْفِرُ لَكَ ‏.‏