It is narrated from Sayyiduna Zayd bin Thabit (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever gives something as an 'umra, it belongs to the one to whom it was given, in his life and after his death. And do not make a ruqba; whoever is given something as a ruqba, he is its heir."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الهبات / 11989