مُسْنَدُ أَحْمَدَ
Musnad Ahmad 2141
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated from Ibn 'Abbas (رضي الله عنه) that the Prophet (ﷺ) said: "Paying in advance for the offspring of what is in the uterus is riba.”
Musnad Ahmad 2145Its isnad is saheeh]