Musannaf Ibn Abi Shayba 6:1013

Hafs ibn Ghiyath narrated to us, from Ubayd Allah ibn Umar, from Nafi, from Ibn Umar, that when he would arrive and some of his children had died, he would say, "Guide me to his grave." So they would guide him to it, and he would go and stand over it and supplicate for him.