Hadith 8:2239
Abu Bakr narrated to us, he said: Hafs narrated to us, from Ash'ath, from Abd al-Malik, from Ibn Sirin, who said: They used to hold the view that if she performed Hajj while she was pregnant, the child in her womb would have a Hajj.
حدثنا أبو بكر قال حدثنا حفص عن أشعث عن عبد الملك عن بن سيرين قال كانوا يرون إذا حجت وفي بطنها ولد أن له حج