Layth bin Sa'd (may Allah have mercy on him) said that Abdullah bin Abbas and Abdullah bin Umar (may Allah be pleased with them) both used to say: Whoever has lent out wealth must pay its zakah every year, when it is with a reliable person.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7620
Ikrimah narrates from Ibn Abbas (may Allah be pleased with them both) that he was asked about the zakah of absent wealth. He said: Pay the zakah of your absent wealth just as you pay the zakah of the wealth that is present. The man said to him: Then the wealth will be ruined? He said: The ruin of wealth is better than the ruin of religion.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7621
Nafi' (may Allah have mercy on him) narrates from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that he used to take the wealth of orphans as a loan, because he considered that safer for it than leaving it deposited, and he used to pay the zakah of their wealth.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7622