It is narrated from Hazrat Anas (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: In Islam, there is no validity to exchange marriages (watay satay) in which no dowry (mahr) has been specified; in Islam, there is no validity to giving poetic similes by naming imaginary beloveds; in Islam, there is no validity to becoming an ally of any tribe; it is also not correct for the collector of zakat to select the best wealth, nor for people to adopt tricks to avoid zakat.