“Those who knowingly allow the King to err deserve the same punishment as traitors.”
Los que dejan al rey errar a sabiendas, merecen pena como traidores.
Quoted in Diccionario ilustrado de frases célebres y citas literarias (1952), by Vicente Vega.
Alfonso X of Castile was a Spaniard, who was the King of Castile, León and Galicia from 30 May 1252 until his death in 1284. During the election of 1257, a dissident faction chose him to be Roman-German king on 1 April. He renounced his claim to Germany in 1275, and in creating an alliance with England in 1254, his claim on Gascony as well.
Alfonso X fostered the development of a cosmopolitan court that encouraged learning. Jews, Muslims, and Christians had prominent roles in his court. As a result of his encouraging the translation of works from Arabic and Latin into the vernacular of Castile, many intellectual changes took place, perhaps the most notable being encouragement of the use of Castilian as a primary language of higher learning, science, and law. Alfonso was a prolific author of Galician poetry, such as the Cantigas de Santa Maria, which are equally notable for their musical notation as for their literary merit. Alfonso's scientific interests—he is sometimes nicknamed the Astrologer —led him to sponsor the creation of the Alfonsine tables, and the Alphonsus crater on the moon is named after him. As a legislator he introduced the first vernacular law code in Spain, the Siete Partidas. He created the Mesta, an association of sheep farmers in the central plain, but debased the coinage to finance his claim to the German crown. He fought a successful war with Portugal, but a less successful one with Granada. The end of his reign was marred by a civil war with his eldest surviving son, the future Sancho IV, which continued after his death. Wikipedia

“Those who knowingly allow the King to err deserve the same punishment as traitors.”
Los que dejan al rey errar a sabiendas, merecen pena como traidores.
Quoted in Diccionario ilustrado de frases célebres y citas literarias (1952), by Vicente Vega.
Si hubiera estado presente en la Creación, habría dado algunas indicaciones útiles.
After studying Ptolemy's treatise on astronomy.; reported in Thomas Carlyle, History of Frederick the Great, book ii. chap. vii. Carlyle wrote that this saying of Alfonso about Ptolemy's astronomy, "that it seemed a crank machine; that it was pity the Creator had not taken advice," is still remembered by mankind, — this and no other of his many sayings.
If the Lord Almighty had consulted me before embarking on creation thus, I should have recommended something simpler.
Quoted/paraphrased by Adam Riess in his Nobel Prize (in Physics 2011) lecture slides on Supernovae Reveal An Accelerating Universe (A Science Adventure Story).
“As quoted in Aire puro para el amor y la amistad Betancourt, Luis Fernando 7a. reim., p. 165.”
Quemad viejos leños, leed viejos libros, bebed viejos vinos, tened viejos amigos.
Burn old wood, read old books, drink old wines, have old friends.
Literal translation.
Variant translations:
Old wood to burn! Old wine to drink! Old friends to trust! Old authors to read! —Alonso of Aragon was wont to say in commendation of age, that age appeared to be best in these four things.
As quoted in Floresta Española de Apothegmas o Sentencias, by Melchior de Santa Cruz (1576), ii. 1. 20.
Alonso of Aragon was wont to say in commendation of age, that age appears to be best in four things, — old wood best to burn, old wine to drink, old friends to trust, and old authors to read.
As quoted in Apothegms (1624) by Francis Bacon, 97.