Three people who get paid twice
Each of them had two claims to satisfy.
ثَلاَثَةٌ لَهُمْ أَجْرَانِ رَجُلٌ مِنْ أَهْلِ الْكِتَابِ آمَنَ بِنَبِيِّهِ، وَآمَنَ بِمُحَمَّدٍ صلى الله عليه وسلم وَالْعَبْدُ الْمَمْلُوكُ إِذَا أَدَّى حَقَّ اللَّهِ وَحَقَّ مَوَالِيهِ
Thalāthatun lahum ajrān: rajulun min ahli-l-kitābi āmana bi-nabiyyihi wa āmana bi-Muḥammad, wa-l-ʿabdu-l-mamlūku idhā addā ḥaqqa-Llāhi wa ḥaqqa mawālīh
“Three have two rewards: a man of the People of the Book who believed in his prophet and believed in Muhammad, and an owned servant who fulfils the right of Allah and the right of those over him.”
Where this comes from
The third is a man who had a slave woman, taught her well, disciplined her well, freed her and then married her. In every case the doubling is for carrying two obligations at once rather than for doing anything extra.
The full narration
Narrated Abu Burda's father: Allah's Messenger (ﷺ) said "Three persons will have a double reward: 1. A Person from the people of the scriptures who believed in his prophet (Jesus or Moses) and then believed in the Prophet Muhammad (ﷺ) (i.e. has embraced Islam). 2. A slave who discharges his duties to Allah and his master. 3. A master of a woman-slave who teaches her good manners and educates her in the best possible way (the religion) and manumits her and then marries her
Source
Ṣaḥīḥ al-Bukhārī · 97
- Agreed upon as authentic (al-Bukhārī / Muslim)