Articles 66, 67 and 115 of the "General Taxes Law" of Spain demand you are able to prove those earnings' source, and legality, and that taxation has been performed for them; for 4 years (theoretically, in practice from 4 and a half to almost 5 and a half, depending on the month when they were earned).
Otherwise, nothing else than that ohwilleke had already answered.
PS: If you have happened to properly declared at the revenue service of Spain that you moved to Germany, that makes them unable to demand taxation for your income (articles 8 and 10 of the main personal income tax law in Spain), from that moment, as is assumed that by default Germany will apply income taxes on you from then on, and you would be by default not under the jurisdiction of the “personal income tax” (IRPF), not enforceable in Germany, but under the “personal income tax for non residents” (IRNR), enforceable while you are living abroad for income considered to been earned in Spain while you are living abroad (article 1 of the "personal income tax for non residents" law), but obviously not for income earned in Germany as that’s the obvious jurisdiction of the German personal income tax.
TL;DR for this section: if you didn’t tell the revenue service of Spain that you were moving abroad (most likely), it’s possible that you might have to prove them that you were living abroad, if they “ask”1 you for proof that that money is not subject to the [Spanish] income tax, but that (proving to have been living abroad) should be easy; and if you had told them that you were moving abroad, back on the day when you were moving abroad (unlikely done, but I think it'd been a good thing to do), it’s likely that they’ll be smart enough to just assume your taxes for that money are most probably OK.
1: Specially subject to articles 136 to 140 of the "General Taxes Law" and annex subsidiary laws.
Hope that helped.
DISCLAIMER: This is not your lawyer, it's a vague (yet informed) entry level reference in order to guide you. Here's no responsibility for any damages caused. If on doubt, always choose to go to your lawyer.