What is the ruling on a pilgrim retaining some of the pebbles collected for throwing the jamarat after his return from Makkah to his city, which is 1400 kilometers away, and is he obliged to return them?

Taking the stones and earth of the Haram is a matter of scholarly disagreement. Some have prohibited it or deemed it reprehensible, while others have permitted it. It is more cautious to return them to the Haram if they were taken from it, especially since the Shafi'is explicitly stated the prohibition of transferring the earth and stones of the Haram outside of it, and the obligation to return them to it.