It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) forbade selling or gifting the right of wala.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 5496
Hadith Gradingحکم دارالسلام:إسناده صحيح ، خ : 2535، م :1506.