Ata bin Abi Rabah (may Allah have mercy on him) said that Sayyiduna Abdullah bin al-Zubayr (may Allah be pleased with him) used to take money from people in Makkah, then write for it to Mus'ab bin al-Zubayr in Iraq, and they would collect it from him. Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) was asked about this, and he too saw no harm in it. It was said to him: What if they take more than that? He said: There is no harm, as long as they take the weight of their dirhams.
(b) This was also narrated from Sayyiduna Ali (may Allah be pleased with him); if it is authentic from him and from Sayyiduna Ibn Abbas (may Allah be pleased with them both), then what is meant, and Allah knows best, is when it is without a condition.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10947