Musannaf Ibn Abi Shayba 13:1180

Abu Bakr narrated to us, he said: Isma'il ibn 'Ulayyah narrated to us, from Ibn 'Awn, he said: Al-Miswar ibn Yazid narrated to us that a woman found a young boy and spent on him until he grew up, then she sought her expenses [back]. So he wrote regarding that to Umar ibn Abd al-Aziz. [He replied] that she should be made to swear an oath that she did not spend on him seeking reward [from Allah]. If she swears, she is compensated.